题目

The world’s African elephants are in serious danger. 【1】 And if we do nothing to put an end to the illegal ivory trade, elephants will be extinct from the wild within the next 20 years.Many believe that an illegal hunter could get ivory without killing the elephant-this is not true. 【2】 And the rest lies beneath the surface like an iceberg（冰山）in water. The tusk is not just bone but rather it is alive, filled with nerves and blood vessels（血管）and when broken off, the tusks would likely become infected and lead to a slow and painful death.However, there is a new form of 下列四个装置中，导线中的电子由左边一极流向右边一极的是（    ）