碳和氢是组成煤的两种主要元素。
参考答案：对
—We could invite John and Barbara to the Friday night party.
—Yes, ________? I'll give them a call right now.[ ]
A. why not
B. what for
C. why
D. what
血液运行主要依赖的是（）
A.心气
B.脾气
C.肝气
D.肺气
E.胃气
