Scientists have concluded that nonsmokers who must______inhale（吸入)the air polluted by to

Scientists have concluded that nonsmokers who must______inhale(吸入)the air polluted by tobacco smoke may suffer more than the smokers themselves.

A．involuntarily

B．instantaneously

C．spontaneously

D．reluctantly

请帮忙给出正确答案和分析，谢谢！