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。

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

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

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

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