森林火灾的燃烧类型分几种？
参考答案：
森林火灾的燃烧类型常分为地下火、地表火和树冠火。
How long ______ you ______ here since you ______ to Beijing?[ ]
A. did; live; came
B. did; live; have come
C. have; lived; came
D. have; lived; have come
掘沟、剥离和采矿三者之间的何关系？
