题目内容：

请根据句意及汉语提示，写出所缺单词。

1.It is _______________(不可能的)to finish reading the book in two days.

2.(妻子)_________________and husbands should look after each other well.

3.We must try our best  to protect the ________________(环境).

4.We’ve learned a lot about HongKong’s past and ________________(现在).