A-A+
A．It influences the surface temperature of Mar
问题详情
A．It influences the surface temperature of Mars.
B．It protects living beings from harmful rays.
C．It keeps a planet from overheating.
D．It is the main component of the air people breathe.
参考答案
正确答案：D
解析：文中的they(指scientists)will have to discover how much nitrogen it possesses，since nitrogen is four fifths of the air we breathe表明，科学家之所以研究火星上是否有足够的氮气是因为氮气是我们所呼吸的空气的主要成分，故D项正确。
