物体（刚体）在两个力的作用下保持平衡的条件是：这两个力的大小相等，方向（），且作用在同一条直线上。
A、相同
B、相反
C、相交
参考答案：B
I watched the man for a long time and wanted to know _______. [ ]
A. whether I have seen him before
B. where I had seen him before
C. that I had seen him before
D. when did I see him
电控汽油机燃油喷射系统一般由（）、（）、（）三个电子系统组成。
