Mack knew this passage by heart.麦克会背这一段。You must keep repeating the lines until they are known by heart.你必须反复朗读这几行一直到能背诵为止.The boy learned the poem by heart.这男孩背下了这首诗....
An earthworm is a terricolous organism.蚯蚓是陆生的生物.The earthworm population had declined by 70 %.蚯蚓数量下降70%.The oral opening in an earthworm is small.蚯蚓的口是很小的....