根据句意用所给词的适当形式填空。
1.Jack usually checks his test paper ____ (careful) before handing it.
2.Mary thinks ____ study) grammar is a great way to learn a language.
3.–What ____ (happen) to Dave on April Fool's Day?  –He was fooled by his friends.
4.Students in this school want to be ____ (volunteer) during this winter vacation.
5.Liu Li was the ____(win) of last year's English Speech Competition in our school.