连枷胸的患者，吸气时软化的胸壁内陷，呼气时则相反。()
参考答案：对
He felt_______ to work for human rights and progress.
A．it his duty
B．his duty
C．that is a duty
D．that is his duty
人走路时，人和地球之间的作用力和反作用力的对数有[ ]
A、一对
B、二对
C、三对
D、四对
