根据下面句子的意思及所给的汉语提示，写出空缺处的单词或词组的正确形式。

1. She was so tired that she fell ____________（睡着的）at her desk.

2. The machine didn't work. Some ____________（工程师）came to help with the mending.

3. He was too busy. He felt he couldn't ____________（抽得出）any more time off work.

4. We did some cleaning and ____________（扔掉）some old things.

5. Don't stand on chairs. Many people ____________（伤着自己）by falling off chairs.

诱导免疫耐受形成的最佳时期是

A．成年期
B．幼年期
C．老年期
D．胚胎期
E．青年期