吗啡的镇痛作用与其激动脑内阿片受体有关。
参考答案：对
The experiment show that proper amount of exercise, if ________ regularly, can improve our health. [ ]
A. carry out
B. carried out
C. to carry out
D. being carried out
企业向外部物流机构所支付的各项费用是指：（）。
A．材料费
B．人工费
C．维护费
D．委托物流成本
