单选题 How is the image of the north polar cap of Mars?
【正确答案】 B
【答案解析】[注释] 见第一段第四句In these views the north polar cap is turned toward the Earth and is clearly visible at the top of each picture.可以用题干中的north polar cap作为信号词在文章中进行扫描来找到这个依据句。