At the beginning of a speech, it is very important to grab the audience’s attention and make them interested in     ________you have to say.    

A．which

B．what

C．that

D．who

焊缝用串列探头进行扫查，主要用于检测（）

A、平行于探测面的缺陷

B、与探测面倾斜的缺陷

C、垂直于探测面的缺陷

D、不能用斜探头检测的缺陷