下面四个图象分别表示四个物体的位移、速度、加速度和摩擦力随时间变化的规律．其中反映物体受力不可能平衡的是（ ）
BC
一 Why didn't you remind him of the possible danger?
一 But what _____ otherwise? He never listens to me. [ ]
A. could I do
B. could I have done
C. should I do
D. must I have done
缺铁性贫血最常见的病因是（）.
A.慢性胃炎
B.慢性肝炎
C.慢性溶血
D.慢性感染
E.慢性失血
