A．FA1 = 0       FA2 = 2 mg       FB1 = 0      FB2 = 2 mg  

B．FA1 = mg      FA2 = mg        FB1 = 0      FB2 = 2 mg  

C．FA1 = 0       FA2 = 2 mg       FB1 = mg     FB2 = mg

D．FA1 = mg      FA2 = mg        FB1 = mg     FB2 = mg      

  • 答案
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