根据句意，用括号中所给词的适当形式填空。
—How old is your son?
—We had a special party for his        birthday last Saturday. (nine)
The dictionary is very        to us students.(help)
Parents always tell their children not to accept any food from a        .(strange)
Don’t be angry with       . He is just a child.(he)
You should give up        because it isn’t good for your health.(smoke)