问题
选择题
You mustn't _______ them everywhere _______ you use plastic bags. [ ]
A. fall; until
B. fall; before
C. drop; while
D. drop; after
答案
答案：D
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You mustn't _______ them everywhere _______ you use plastic bags. [ ]
A. fall; until
B. fall; before
C. drop; while
D. drop; after
答案：D