They _________  the plane, or perhaps they have been prevented from coming for some reason.

A．can have missed

B．can have lost

C．may have missed

D．may have lost

下列有关目前世界城市化进程的叙述，正确的是[ ]

A．发达国家城市人口比重大、增长快  

B．发达国家城市人口比重小、增长慢

C．发展中国家城市人口比重小、增长快  

D．发展中国家城市人口比重大、增长慢