液压系统压力正常执行元件无动作的原因及排除方法是什么？
参考答案：
把下列句子变为一般疑问句，并作肯定和否定回答，每空一词。
1. He'd like a medium bowl.
______ ______like a medium bowl?
Yes, he ______.
No, he ______.
2. There are some boys in the classroom.
______ ______ ______ boys in the classroom?
Yes, ______ ______.
No, ______ ______.
3. They're playing football on the playground.
______ they _______ football on the playground?
No, _______ _______.
Yes, _______ _______.
4. The weather is nice and cool.
______ the weather nice and cool?
Yes, ______ _______.
No, ______ _______.
5. They were busy yesterday afternoon.
______ they busy yesterday afternoon?
简述增值税专用发票开具时限的要求
