问题
单项选择题
在用经验法整定调节器PB和Ti参数时，当阶跃改变给定值后，其超调量σP=0，且被控量需很长时间才能稳定在给定值上，应使（）。
A.PB↑，Ti↑
B.PB↑，Ti↓
C.PB↓，Ti↑
D.PB↓，Ti↓
答案
参考答案：D
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在用经验法整定调节器PB和Ti参数时，当阶跃改变给定值后，其超调量σP=0，且被控量需很长时间才能稳定在给定值上，应使（）。
A.PB↑，Ti↑
B.PB↑，Ti↓
C.PB↓，Ti↑
D.PB↓，Ti↓
参考答案：D
I hadn’t even got a chance to enter the store before an African American woman approached me and asked if I would help her return an item. The item she has ___ __ was intended for her daughter, but she had already received a similar one. The lady ___ __ to exchange the item for something else in the store but she was told she needed an ID or the deal could not take place. I went to the __ __ with the woman so we could use my ID. The sales associate immediately started ___ ___ her of asking the first random person she saw to help her. Although that was true , I didn’t understand why it mattered. After all, not everyone is given the opportunity to __ __ an ID in this country. Then, we asked to speak with a manager, who explained that there was no way to return the item without a receipt and then went on to say the woman could not ___ ___ she purchased the item. “If I , a young white female, were to enter the store and request you to make an exchange without a receipt, I would not be ___ __ the privilege--- as I have proof from the past.” I said. He must have realized at that moment what he had done, because he ___ __ to exchange the item. There are many valuable lessons in the story. The first is to help a stranger in need. I hesitated when the woman asked for my help, but ___ ___ in my hand I asked myself, “ Why not? What valid reasons do I usually have?” I had none, so I helped her. The second lesson is not to judge a book by its cover. The woman looked poor, but she ___ __ the same treatment as anyone else does.
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