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