The atmosphere certain gases mixed together in definite proportions.

选择一项:

A.
is made up


B.
composes of


C.
consists of
出自:国家开放大学-大学英语1

完成拼图验证

按住下方滑块,将拼图拖到缺口处后松开。

拼图背景,将小拼图拖到缺口处
向右拖动滑块