People ____ less tolerant of smoking in public places these days. [ ]

A. become

B. have become

C. will become

D. are becoming

地质学研究表明，原始大气成分与现在大气相比的明显差别是：原始大气中没有[ ]

A．氧气　　

B．氢气　　

C．水蒸气　　

D．甲烷