According to the recent report made by the government, the number of visitors who have traveled to the earthquake-hit areas like Wenchuan in Sichuan has ______20,0000, ________to promoting their awareness of the disaster in hisrory.

A．reach; contribute

B．reached; contributed

C．got; contributing

D．reached; contributing

补偿中子是测量（）。

A.热中子

B.超热中子