单项选择题

now the problem of air pollution is becoming critical. it__________ an immediate solution.

A. calls off
B. calls for
C. calls up
D. calls on
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单项选择题
you ________ a pass to enter that building.
A. need get
B. need getting
C. need got
D. need to get
判断题
发现教学的基本假设：通过正确地回答问题，人们可以得到积极的强化，因此更可能重复学习到的行为。()
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