How much does it cost for five stamps？
A. 20 cents.
B. $1.00
C. $2.20.
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半导体二极管的重要特性之一是__________。
A. 温度稳定性
B. 单向导电性
C. 放大作用
D. 滤波特性
Why was Dora late？
A. She didn't know the time.
B. She forgot her class.
C. She didn't catch the bus.
二阶压控电压源低通有源滤波器通带外幅频响应曲线的斜率为_________。
A. 20 dB／十倍频程
B. -20 dB／十倍频程
C. 40 dB十倍频程
D. -40 dB／十倍频程
What is the man's problem？
A. He has to find two jobs to support himself.
B. He can't decide whether to take a science course or not.
C. He can't study full time this year.
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