单项选择题

The machine can't be made perfect overnight; in fact, it should be improved ______.

A．one after another
B．by turn
C．right away
D．step by step
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单项选择题
We can hardly avoid making any mistakes in our work ______ hard we try.
A．whatever
B．how
C．no matter
D．however
单项选择题
If you speak slowly and clearly, the students will ______ the meaning.
A．take on
B．take down
C．take in
D．take back
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