Figure Problem shows a standing wave on a 2.0 m long string that has been fixed at both ends and tightened until the wave speed is 40 m/s . The frequency is _____________ .【图片】
A.
40Hz
B.
80 Hz
C.
160 Hz
D.
20 Hz
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【单选题】—Do you like table tennis or cycling? —______. [ ]
【简答题】听对话,给下列句子标号。 ( ) Can you set the table? ( ) Can you wash the clothes? ( ) No, I can't, but I'd like to have a try! ( ) Yes, I can. I can do the dishes, too.