D．possibly due to the activity of the sun

　　解析：选D　细节理解题。文章第三段提及这一现象时讲到，科学家们认为：这一现象的产生是因为到目前为止自然界对天气的影响要大于人类对天气的影响。而究竟是哪种自然力量对天气的影响最大呢？文章第四段第一句话给出了答案：其中一个可能就是太阳的活动。D项与此意相符。

　　8．What does the underlined word "exceeded" mean?

　　A．To be the same as.

　　B．To be slower than.

　　C．To be better than.

　　D．To be bigger than.

　　解析：选D　词义猜测题。由倒数第一段的"This seems to have a greater effect on the distribution of the earth's atmospheric pressure, and consequently on wind circulation (循环)．"可看出自然界对天气的影响要大于人类对天气的影响。

　　C

　　Due to climate changes, Arctic ice is breaking up earlier in the spring, and its area is decreasing. This is creating problems for polar bears that make their homes off northern Alaska and in Hudson Bay.

　　Polar bears off Alaska normally hunt and raise their young on ice sheets that float on the ocean. But as the ice has melted, the polar bears have been forced to spend more time on land. There, they have begun to frequent beaches, feeding on the remains of whales caught by native hunters. For polar bears, this food is less nutritious than seals that they normally catch on ice sheets. The shrinking (减少) ice has also forced more polar bears into the ocean. In the past, they only had to swim short distances between ice sheets. But as the ice has shrunk, polar bears have been forced to swim longer and longer distances in the open ocean. This poses a severe danger during rough weather, and an increasing number of drowned polar bears have been observed.

In Hudson Bay, the ice breaks up three weeks earlier in the spring now than it did 20 years ago. Polar bears on Hudson Bay fast (绝食) during the summer, waiting for ice to form in the fall to hunt. Every year, the summer gets longer, and the bears get skinnier. Over the past 25 years, the average weight of the female bears has dropped 68 kg. This loss affects their ability to reproduce,