交流发电机是利用硅二极管的单项导电特性把交流电转化为直流电。
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---Who’s that? ---______ is Tom.
A. It
B. He
C. She
D. Her
Give ______ some boxes.
A. they
B. their
C. them
D. theirs
These are ______ chairs.
A. students
B. students'
C. the student's
D. students's
---What’s that? ---It’s ______ magazine.
A. a
B. an
C. the
D. /