石油化工冷却水系统中用腐蚀监测的监测换热法，其试验时间最少为（）天
A.10
B.30
C.60
D.90
参考答案：B
_________ is a fact that English is being accepted as an international language.
A．There
B．This
C．That
D．It
分组选配法
