题目

 如右图所示，F1=F2=1N，分别作用于A、B两物体上，且A、B均保持静止，则A和B、B和地面之间的摩擦力分别为（     ）A. 1N、1N                  B. 2N 、0C. 1N、0                   D. 2N、1N 答案：CEach time ______ they met, they would talk long hours together.A. which B. when C. during D. /