金属的晶体结构不同，机械性能也不同，如γ-Fe比α-Fe的塑性好，强度低。
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My teacher knows more than___.
A. my uncle knows
B. my uncle does
C. they know
D. they don't know
She ___ Shanghai for a year.
A. has been away from
B. left
C. has left
D. has been leaving
I think natural beauty ___ the best.
A. was
B. is
C. were
D. be
What ___ when I saw you yesterday?
A. did you do
B. were you doing
C. you were doing
D. you did
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