根据汉语或首字母提示写出单词，使句子完整。将答案直接写在横线上。

1. A library keeper is another way of saying a l________.

2. The p_______ of China is up to 1.3 billion.

3. Planting trees can help to make our________ (环境) clearer and more beautiful.

4. China is a great country ________ (有) a long history.

5. Our headmaster often surfs the________ (英特网) for useful information.

婴儿辅助食品添加步骤是：出生2周后加__________，4个月后加__________、__________，6个月后加__________，__________。