1. 用bad,一般感官动词后面都会用形容词.
2. is also,系动词后面加副词的吧.
3. 这要看的.
It's difficult to是一句句子,比如It's difficult to understand.很难理解.
但是如果it不是主语而是宾语的话那么就要用it,没有is,因为这句句子已经前面有谓语了,一句句子不能出现两个谓语.比如I feel it difficult to understand.这里是I feel .已经是一句句子了.后面只能加宾语.原意是I feel (to understand) difficult.