Question

17. ―What a pity! Their experiment is a failure.

―They    better under more favourable conditions.

A. should have done    B.  could have done

C.  must have done      D.  may have done

Answer 1

17.   B考查含蓄的虛擬條件句。句意："真遺憾！他們的實(shí)驗(yàn)失敗了。""在更加有利的條件下，他們本能做得更好。"這里under more favorable conditions是一個(gè)隱含的虛擬條件句， 相當(dāng)于if they had been under more favorable conditions。 這是和過(guò)去事實(shí)相反的虛擬條件句，所以主句用could have done的形式。could have done表示過(guò)去原本能夠做某事而實(shí)際上并沒(méi)有做。所以選B。