升压斩波电路的输出侧必须并联大电容，降压斩波电路的输出侧可以并联大电容，也可以不并联大电容。（）
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Why is reading so difficult for Bradley?
A. Because it is difficult for him to focus on reading.
Because he doesn't like reading at all.
What is Bradley for by working extra hard in books?
A. For acquiring knowledge from books.
B. For getting high marks in the exam.
What is Bradley's attitude towards Thomas?
A. Bradley believes Thomas can do well in reading.
Bradley thinks Thomas shouldn't hate books.
“搭便车”现象是对下面哪个问题的一种形象的描述？（ ）
A. 社会福利问题
B. 公共选择问题
C. 公共产品问题
D. 垄断
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