If the US____more homes for the poor in the 1950s, the housing problem _____so serious now.
A.built; is
B.had built; would not have been
C.had been building; would not be
D.had built; would not be
正确答案是D
If the US____more homes for the poor in the 1950s, the housing problem _____so serious now.
A.built; is
B.had built; would not have been
C.had been building; would not be
D.had built; would not be
正确答案是D