题目内容：

根据所给汉语提示将下列句子补充完整（每空一词）。

1.He often ________ ________ some useful advice. (提出)

2.It’s very dangerous to ________ _______ _______ these viruses without any protection. （暴露在…之下）

3.He ________ the apples _______ four parts. (分成)

4.Plastics have ________ ________ ________ ________many conventional (传统的) materials.   (代替)

5.It was so dark he ________ ________ ________her at once. (看不见)