根据句意，在相应的横线上，写出括号内所给单词的适当形式。

小题1:An advantage of using the solar energy is that it won’t create any        (pollute).

小题2:Our headmaster is the        (strict) with us among the teachers who teach us.

小题3:What an          (enjoy) journey they had the day before yesterday!

小题4:Those volunteers always think more of others than of          (they).