题目

下列离子方程式表示的是盐类的水解且正确的是() A . HS－＋H2O H3O＋＋S2－ B . HS－＋H＋=H2S C . CO32-＋2H2O H2CO3＋2OH－ D . Fe3＋＋3H2O Fe(OH)3＋3H＋ 答案：D— Where are the students? How could they keep us waiting for so long?  — They started an hour ago and they________ be here in fifteen minutes, I think. [     ]A. can  B. wouldC. should  D. must