She didn't know________.A.what she could do itB.what to do itC.what she can doD.how to do it

选择D吧 她不知道怎样做（它）.
一般这一类的是这么记的.she did't know what to do .do 后面没有宾语it 那么用what.其实what就是do的宾语.（她不知道做什么）.
还有一种是就是这个选择she didn't how to do it.do后面有宾语it,就选择how表示方式,怎么做的意思.（她不知道怎么做这件事）
另外 what to do 和how to do 都是疑问词+to do （动词不定式）的一个用法.

D
A、B最后的it都是阑尾，C时态不对。

D.
A.B后去掉it 就对了，C时态不对，应该是what she could do.所以选D。
通常用法是what to do How to do +宾语

D.how to do it 。有what时do后不能有it，didn't是过去时C改成could才对

选C。 A、B、D选项都要去掉it。。
She didn't know what she could do.
她不知道怎么办。
望采纳，祝开心~！

D,语序不改变，what还真没见过怎么to do的，呵呵

C. AB中的it 都是多余的 D中没有how to do的说法

C.what she can do

She didn't know________.
A.what she could do it
B.what to do it
C.what she can do
D.how to do it
选项是D

D
宾语从句
可以用
What to do
How to do
How to do it
What she could do
这四种情况

D 他不知道如何做
how to do it
what to do

选D A和B中what 和 it 指代重复 C应该为could 前后时态要相同