A、 To examine the chemical elements in the Ice Age.
B、 To learn what' s been happening on the sun' s surface
C、 To analyze the composition of different trees.
D、 To find out the origin of carbon-14 on Earth.

【正确答案】 B

【答案解析】解析：细节辨认题。短文第二句指出Scientists are using tree rings to learn what’s been happening on the sun’s surface for the last ten thousand years，故科学家研究树年轮的目的是为了调查在过去一万年前太阳表面到底发生了什么。所以选项B正确。

A、 The life cycle of trees.
B、 The number of trees.
C、 The intensity of solar burning.
D、 The quality of air.

【正确答案】 C

【答案解析】解析：细节辨认题。短文中指出he found carbon-14 levels change with the intensity of solar burning，故地球上碳14的含量受太阳燃烧强度的影响。所以选C。

A、 It affects the growth of trees.
B、 It has been increasing since the Ice Age.
C、 It is determined by the chemicals in the air.
D、 It follows a certain cycle.

【正确答案】 D

【答案解析】解析：事实细节题。根据短文最后一句The scientists concluded that the solar wind activity must follow the same cycle，可知太阳风的活动遵循着一个相同的周期。所以选D。