用所给单词的适当形式填空
【小题1】Don't you think ________ (ride) a bicycle on a sunny day is fun?
【小题2】When I got home, I found the gate of my house ________ (lock)．
【小题3】It's dangerous ________ (stay) outside late by yourself.
【小题4】You should knock on the door before ________ (enter) the teachers' office.
【小题5】Though my grandma is over 80, she can look after ________ (she)．