32. 一You were brave enough to raise objections at the  meeting．

一 Well, now I regret_________ that．

A．to do

B．to be doing

C．to have done

D．having done

铁酸钠（Na₂FeO₄）是一种新型净水剂，铁酸钠中铁元素的化合价是（　　）

A．+2

B．+3

C．+5

D．+6