区别甲烷、氧气、二氧化碳、空气最简单的方法是[ ]

A．用燃着的木条

B．闻气体的气味

C．观察气体的颜色

D．倒入适量石灰水

The patient says he dreads ______ neighbors to carry him and his wheelchair up the stairs to his tenth-floor apartment when the elevator goes out.

A．asking
B．to ask
C．being asked
D．to be asked