So many natural disasters are believed___________over the recent years because of the frequent unreasonable mankind activities.

A．to have come about

B．to come about

C．coming about

D．to be coming about

( )是反映社会经济现象在一段时期内活动结果的总量指标。

A．时点指标

B．平均指标

C．相对指标

D．时期指标