题目内容：

根据句意和汉语注释，在答题卡标有题号的横线上，写出单词的正确形式。

1.I’m so helpful that it's my ______ (please) to help give a seat to somebody in need.

2.The final-exam is coming. The students are ______ (active) revising for tests.

3.Because many factories pour waste water into the river, we must take action to change the______ (pollute) environment.

4.It’s known to all that this trail is the ______ (far) one we have ever walked.