题目内容

u=-100sin(6πt+10°)V超前i=5cos(6πt-15°)A的相位差是25° ( )

A. 对
B. 错

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4cos2πt 是周期T=1S、频率f=1Hz的正弦波。( )

A. 对
B. 错

This is ___ reading-room.

A. the student's
B. student's
C. students
D. the students

How many___ would you like?

A. paper
B. bread
C. pieces of papers
D. pieces of bread

He was praised for his ___.

A. brave
B. bravery
C. bravely
D. great brave

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