The machine can't be made perfect overnight ；in fact it should be improved ( ) .
A.one by one
B.step by step
C.place by place
D.one after another
正确答案是B
The machine can't be made perfect overnight ；in fact it should be improved ( ) .
A.one by one
B.step by step
C.place by place
D.one after another
正确答案是B