根据句意，用括号内所给动词的适当形式填空。
1. His father has decided _________ (go) to Suzhou.
2. Understanding the passage well first is the best way _________ (recite) it.
3. It's difficult for such a young child _________ (work) out the problem.
4. Why do you suggest _________ (visit) the museum?
5. Mr Green enjoyed _________ (play) soccer when he was young.