振荡器具有稳定输出的原因，是振荡系统中有非线性器件存在。
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Why does the writer believe thinking for oneself is not popular?
A. Because it takes too much time.
Becuase it doesn't lead to progress.
C. Because it is regarded as dangerous.
D. Because only a few people are able to do it.
In the opinion of the writer, how often are people interested in your ideas?
Always.
B. Often.
C. Never.
D. Hardly ever.
Who first made the writer realize that thinking for oneself is important?
A. The writer's parents.
B. The writer's friend, Sarah.
C. The writer's maths teacher.
D. The manager of an oil company.
How did the writer feel when she was asked to write "the sum of a number"?
A. Pleased, because it was an easy question to answer.
Bored, because she wasn't interested in maths.
Confused, because she didn't understand the question.
D. Worried, because she was the only one who didn't know the answer.
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