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【单选题】
An open pipe of air supports standing waves at frequencies of 300 Hz and 400 Hz. There are no other frequencies between these two. What is the frequency of the second harmonic of this tube?A.
100 Hz
B.
200 Hz
C.
400 Hz
D.
600 Hz
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举一反三
【单选题】Activities and standards that an organization must successfully perform or achieve to effectively carry out its mission are called:
A.
goals.
B.
strategies.
C.
tactics.
D.
responsibilities.
【单选题】carry out
A.
to take away
B.
to perform or complete
C.
to give or offer something
D.
to suggest an idea
【单选题】The present policy in China has ______ further co-operation with many other countries.
A.
elected
B.
entertained
C.
entered
D.
enabled
【单选题】Finnish President said Finland-China relations had progressed ______ with fruitful co-operation in new and high-tech fields.
A.
peacefully
B.
highly
C.
quietly
D.
smoothly
【简答题】A _________ is a machine which is programmed to move & perform certain tasks automatically. It is a mechanical device with a control system that makes it able to carry out tasks automatically.
【简答题】carry out/ perform a contract
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