取景器主要有旁轴取景器、单镜头反光式取景器和双镜头反光式取景器。()

对于高权威的传达者，发出的信息与个人原有态度差异较大时，引发的态度改变量最大。() 点击查看答案&解析

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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