系统抽真空时需隔离循环氢压缩机，防止抽真空期间被损坏的部件是：（）。
A、密封
B、气阀
C、活塞
D、十字头
参考答案：A
根据句意用适当的人称代词填空。
1. This is Linda. _____ is my friend.
2. This is my daughter. _____ is ten
3. —What's this?
—_____ is a pen.
4. This is John. _____is my brother.
5. —Are those your friends?
—Yes, _____ are.
6. —Are _____eleven years old?
—No, I'm ten.
7. —Are you and Tom good friends?
高校毕业生怎样提升自主创业的能力？
