Jack wasn't saying anything, but the teacher smiled at him ________he had done something very clever. [ ]

A. as if      

B. in case

C. while      

D. though

为了提高测试的效率，应该( )。

A．随机选取测试数据

B．取一切可能的输入数据作为测试数据

C．在完成编码以后制定软件的测试计划

D．集中对付那些错误群集的程序