主语从句的题,15._____ is a pity that he should feel so upset.DA.Wh

主语从句的题,
15._____ is a pity that he should feel so upset.D
A.What B.That C.He D.It
16._____ a spoonful of soil can tell us so much about the structure and early
history of the moon.
A.Remarkable B.Quite remarkably C
C.It is remarkable that D.It is remarkable
麻烦给个详细的点的解析,比如第一题为什么选D,为什么不选别的.