Why does the Queen have two birthdays?
A. She can do anything she wants because she’s the Queen.
B. She wants to get a lot of gifts.
C. She has an official birthday when the weather is better.
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Why do British spies carry umbrellas?
A. They use them to keep themselves hidden from view.
B. They use them to protect themselves.
C. They use them to look cool.
Guess what the expressions mean in Chinese.
在放大电路中测得一只三极管三个电极的电位分别为2.8V、3.1V、1V，则这只三极管属于。
A. 硅PNP型
B. 硅NPN型
C. 锗PNP型
D. 锗NPN型
当晶体管工作在截止区时，发射结电压和集电结电压应为。
A. 两者都反偏
B. 前者正偏、后者反偏
C. 两者都正偏
D. 前者正偏、后者也正偏
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