题目

 ______deep down in the earth, the dead forests rotted away and became coal. A. Burying         B. Buried           C. To bury          D. Having buried 答案：B14．引起自发性人口迁移的最根本原因是（　　）A．自然环境因素B．婚姻家庭因素C．经济因素D．政治因素