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...
石灰岩常用于建筑.Limestone is often used in building construction.石灰岩上有许多缝隙，故而树根能从岩洞顶部长出来。The limestone is sufficiently fissured for tree roots to have breached the roof of the cave.当地石灰岩渗透性很强。The local limestone is very porous....