Поставьте глагол в соответствующую форму инфинитива. 1. they made him (to wait - simple infinitive active) for an hour. 2. it could (to use - simple infinitive passive) in colloquial english. 3. he was sad (to hurry - perfect infinitive active). 4. there are a lot of problems (to solve - simple infinitive passive).
2. It could be used in colloquial English.
3. He was sad to have hurried.
4. There are a lot of problems to be solved.