The mountains here are all covered up with trees.中为什么要把up去掉?

______those mountains will be covered with trees. It __________ last night for all the trees are covered with three mountains are covered with snow,tower over the land. 几年之内,这些山脉将被树木覆盖 The mountains will be covered with trees ___ 英语翻译英语翻译,不要机翻!The river whose banks are covered with trees i the river whose banks are covered with trees is very long,这个 Three fourths of the land____ with trees.A.are covered B.is They are running _____ the trees up into on of in a few __time, those mountains will be covered with trees. I believe that those mountains will be covered with trees in Til the walls are goin’ up in smoke with all our memories The company has a good year with production up.这句话中up为什么是副词,