--- ________ I remind you of is to return the book to our English teacher.  

---I will give it to him _________  I see him.   

A．That; immediately

B．What; directly

C．What; while

D．Whether; once

应用X射线荧光光谱分析轻元素时，由于轻元素（）所以要选用粗准直器。

A.潜线固有灵敏度高

B.潜线固有灵敏度低

C.潜线宽度窄

D.潜线宽度宽