Complex subject is used in the following cases:
- After the verbs used in CO (perception, mental activity), but their main verbs are in the passive voice. F.e. She is said to fall in love. You are supposed to know grammar.
- After such word groups: to be sure, to be certain, to be likely, to be unlikely, to be not likely. F.e. He is likely to come in time.
- After such verbs in the active voice: [seem, appear, happen, prove, turn out]. F.e. He proved to be a real friend.
