如圖，列車上有出售食品的手推車.若貨物在車內(nèi)擺放均勻，當(dāng)前輪遇到障礙物A時，售貨員向下按扶把，這時手推車可以視為杠桿，支點是_____（寫出字母）；當(dāng)后輪遇到障礙物A時，售貨員向上提扶把，這時支點是____（寫出字母）.
C，B 
（1）當(dāng)前輪遇障礙物A時，售貨員向下按扶把，這時手推車可看成杠桿，支點是C點；
（2）當(dāng)后輪遇到障礙物A時，售貨員向上提扶把，這時支點是B點，顯然動力臂大于阻力臂，此時手推車可看成是省力杠桿
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