作用力与反作用力大小相等，方向相反且作用在一条直线上，因此能将作用力与反作用力看成一平衡力系而互相抵消
参考答案：错
— How was your trip abroad?
— Great. The only pity is that I _____ to buy some gifts for my friends. [ ]
A. forgot
B. forget
C. would forget
D. was forgetting
从提高温差的角度考虑，冷、热流体最好采用（）。
A、并流
B、逆流
C、错流
D、以上均错误
