i don't know how to do it.为何要加It?而what to do 后则不加it?

i don't know how to do it.为何要加It?而what to do 后则不加it? I don't know ( ).A.what to do it B.how to do it C.what to do I really don't know -----with it.A .what to do B.how to do 选 I don't know "What to do 和 I don't know "How to do it"?哪个句子是 Mary doesn't know how to do it.i don't either 为何不用neither i don't know how to do it句型转换 7.I don’t know _________.A.what to do it B.how to do it C.wh I don't know ------it today.1.what to do 2.how to do 3.to do 找错----Sorry,I don't know what to do it 改错：I don't know what to do it. i don't know when to do it.为啥要加it?而 when to go后则不需加别的啥呢? I really don`t know_____ A.what to do it B.how to do C.what