be+adj+to do sth是不是都用it做形式主语?

问题描述:

be+adj+to do sth是不是都用it做形式主语?
动词不定式做宾补吗?

be+adj+to do sth是用it做形式主语,动词不定式是真正的主语,如
It's important to learn English well .= To learn English well is important .