我有几个名词性从句的题,1.___ has helped to save the drowing girl is wor

我有几个名词性从句的题,
1.___ has helped to save the drowing girl is worth praising.
A.Who B.The one C.Anyone D.Whoever
2.Someone is ringing the doorbell.Go and see____.
A.who is he B.who he is C.who is it D.who it is
3.___ made the school proud was ____ more han 90% of the students had been admitted to key universities.
A.What,because B.What,that C.That,what D.That,because
4.A modern city has been set up in ___ was a wasteland of ten years old.
A.what B.which C.that D.were
答案是DDBA.请问选择的原因是什么?