Choice C is the best answer. The author explains that a “powerful volcano” erupted around 750 years ago and caused “a centuries-long cold snap known as the Little Ice Age” (lines 1-3). The author then states that a group of scientists believe the volcano Samalas was this “powerful volcano,” and she explains how the scientists’ research supports this claim (lines 17-78).

Choices A, B, and D are incorrect because they do not identify the main purpose of the passage.

Choice B is the best answer. The author begins the passage by explaining how the Little Ice Age was a “centuries-long cold snap” that was likely caused by a volcanic eruption (lines 1-3). The author then explains how scientists used radiocarbon analysis to determine when the Little Ice Age began and how a volcanic eruption triggered the cooling temperatures (lines 17-25).

Choices A, C, and D are incorrect because the passage does not criticize a scientific model, offer a new method of measuring sulfates, or shift from the use of radiocarbon dating to an examination of volcanic glass.

Choice A is the best answer. In lines 17-25, the passage shifts focus from describing a recorded event to providing evidence that the Little Ice Age was likely caused by a volcanic eruption. The passage states that scientists used “radiocarbon dating of dead plant material from beneath the ice caps on Baffin Island and Iceland, as well as ice and sediment core data” to determine when the Little Ice Age began and how it was connected to the “mystery” volcanic eruption.

Choices B, C, and D are incorrect because they do not provide the best evidence that the passage shifts focus from a description of a recorded event to its likely cause. Choices B, C, and D all focus on the scientists’ research but do not explain what caused the Little Ice Age.

Choice D is the best answer. According to lines 5-8, “That a powerful volcano erupted somewhere in the world, sometime in the Middle Ages, is written in polar ice cores in the form of layers of sulfate deposits and tiny shards of volcanic glass.” The phrase “is written in” reinforces the idea that the polar ice caps contain evidence of the volcanic eruption, and that scientists can interpret this evidence by examining the “sulfate deposits and tiny shards of volcanic glass.”

Choices A, B, and C are incorrect because the author does not use the phrase “is written in” to demonstrate the concept of the hands-on nature of the scientists’ work, highlight the fact that scientists often write about their work, or underscore the sense of importance scientists have about their work.

Choice A is the best answer. The scientists believe the volcano Samalas, located in Indonesia, was most likely the medieval volcanic eruption (lines 33-35). The eruption likely occurred near the equator because an equatorial location is “consistent with the apparent climate impacts” the scientists observed (lines 61-67).

Choices B, C, and D are incorrect because the scientists do not suggest that the medieval volcanic eruption was located in the Arctic region, the Antarctic region, or Ecuador.

Choice D is the best answer. In lines 61-64, the author cites geochemist Gifford Miller’s findings that provide evidence that the medieval volcanic eruption most likely occurred in Indonesia near the equator: “It’s not a total surprise that an Indonesian volcano might be the source of the eruption, Miller says. ‘An equatorial eruption is more consistent with the apparent climate impacts.’”

Choices A, B, and C are incorrect because they do not provide evidence that the medieval volcanic eruption most likely occurred in Indonesia near the equator. Rather, choices A, B, and C focus on the medieval volcano’s power, impact, and magnitude.

Choice C is the best answer. In lines 68-71, the author states, “Another possible candidate—both in terms of timing and geographical location—is Ecuador’s Quilotoa, estimated to have last erupted between 1147 and 1320 C.E.” The phrase “another possible candidate” implies that the scientists believe that in the Middle Ages a different volcanic eruption, such as an eruption from the volcano Quilotoa, could have been responsible for the onset of the Little Ice Age.

Choices A, B, and D are incorrect because the phrase “another possible candidate” does not imply the frequency or effects of volcanic eruptions, or that some volcanoes have large calderas.

Choice D is the best answer. In lines 71-75, the author explains how Lavigne’s team proved that Quilotoa’s eruption did not cause the Little Ice Age: “But when Lavigne’s team examined shards of volcanic glass from this volcano, they found that they didn’t match the chemical composition of the glass found in polar ice cores, whereas the Samalas glass is a much closer match.” These findings show that Samalas, not Quilotoa, was responsible for the onset of the Little Ice Age.

Choices A, B, and C are incorrect because they focus on the difficulty of identifying the volcano responsible for the Little Ice Age, the magnitude of the volcanic eruption, and the researchers’ experiment.

Choice C is the best answer. The data in the figure show the greatest belowaverage temperature variation occurred in 1675 CE, as the temperature reached a variation of −1.0° Celsius. Choice A is incorrect because the figure shows that the temperature in 1200 CE was above average (+0.25° Celsius). Choices B and D are incorrect because the below-average temperature variation reported in 1675 CE (at −1.0° Celsius) was greater than the below-average temperature variation reported for 1375 CE (around −0.25° Celsius) and 1750 CE (around (−0.5° Celsius).

Choice B is the best answer. The passage says that the Little Ice Age began “about 750 years ago” (line 1) and that “the cold summers and ice growth began abruptly between 1275 and 1300 C.E.” (lines 23-24). The figure indicates that average temperatures in central England began to drop around 1275 CE, and this drop in temperatures continued “through the 1700s” (line 32).

Choices A, C, and D are incorrect because the passage and figure do not indicate that the Little Ice Again began around 1150 CE, just before 1500 CE, or around 1650 CE.

Choice A is the best answer. The figure shows that the greatest cooling period of the Little Ice Age occurred between 1500 and 1700 CE; it also shows that the greatest warming period of the Medieval Warm Period occurred between 1150 and 1250 CE. Therefore, the Little Ice Age’s greatest cooling occurred a couple of centuries, or “hundreds of years,” after the temperature peaks of the Medieval Warm Period.

Choices B, C, and D are incorrect because the figure does not focus on equatorial volcanic eruptions, pyroclastic flows, or radiocarbon analysis.