请你根据句意及所给首字母提示，补全单词。

1.We should try our best to protect the e_________.

2.There are four s_________ in a year, spring, summer, autumn and winter.

3.She is a careful girl, so she made few m_________ in the exam.

4.My brother joined the army (军队), because he wanted to be a s_________ in the future.

5.The p_________ of China is over 1.3 billion (十亿).

在生产实践中，人们常常利用无性生殖来栽培农作物和园林植物，下面选项中不属于利用无性生殖来栽培的是[ ]

A．葡萄的扦插        

B．苹果的嫁接  

C．植物的组织培养      

D．玉米种子长成玉米