We should plant many trees on the mountains．我们应该在山上种许多树。Many trees should be planted on the mountains． 应该在山上种许多树。Teenagers should be allowed to go out with their friends.应该允许青少年和朋友外出。 The children should be allowed to go to the movies with friends on Friday nights. 孩子们应当被允许星期五晚上和朋友们一起去看电影。 Tables can be made of stone. 桌子可由石头做成。Waste paper should not be thrown here．废纸不应该扔在这里。Should it be done by Li Ming? 这件事应该是李明干吗？够了吗？？？
