若用红光照射某金属，不能产生光电效应，于是有人用透镜将光聚焦到该金属上，照射相当长时间，欲使该金属产生光电效应，试问此人的目的能否达到？
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What are tips to improve our listening according to Lucy?
A. listen to a wide range of sounds because there are varitions of sounds.
B. watch TV or each program twice. Don't be afraid of replaying it again and again.
C. don't translate, just to get the content and general meaning of it.
D. Pick a book you like and Listen then read
E. Practise as much as possible, use the time when you are cooking, taking bus or subway home.
F. Learn speech patterns, like reductions, contrctions...
E700变频器参数中,高速的参数是( )。
A. P4
B. P5
C. P6
D. P7
三菱变频器中参数P2用于设定( )。
A. 上限频率
B. 下限频率
C. 基准频率
D. 加速时间
在分拣单元中,电动机的转速是由______________控制的。
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