Only when______ can the postal code system achieve its full efficiency.
A. all the post offices in the country have the fight machines
B. all the post offices have trained staff
C. most post offices have the right machines
D. most post offices have trained staff
A mother will affect her unborn baby if______.
A. she is emotionally shocked
B. she has a good knowledge of inheritance
C. she takes part in all kinds of activities
D. she sticks to studying
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