Ag-DDC光度法测砷时，三乙醇胺起何种作用( )。

A．(A) 有机酸

B．(B) 有机碱

C．(C) 络合剂

D．(D) 氧化剂

One morning my patience was growing thin during Mark talked once too often, and then I made a novice-teacher’s mistake.

A. when

B. as
C. while
D. whenever