题目

下列不属于鸟类适于飞翔的结构特点是（ ）       A．身体呈流线型       B．前肢变成翼       C．陆地产卵       D．骨骼轻、薄、坚固，有些骨中空 答案：CWe should keep the earth _________ and stop _________ it.A.clean; polluting B.to clean; polluting C.clean; to pollute D.to clean; to pollute