7岁的孩子中1/4以上都不会正确地做加法运算。More than a quarter of seven year-olds cannot add up properly.你谅必在商店里见过现金收入记录机,它基本上只能做加法运算.In shops you will have seen cash registers which basically can only add.这个小女孩不太善于做加法.The little girl is no...