什么叫泥石流?
参考答案:
泥石流是由于降水(暴雨、冰川、积雪融化水)产生在沟谷或山坡上的一种挟带大量泥砂、石块和巨砾等固体物质的特殊洪流,是高浓度的固体和液体的混合颗粒流。
What he has done is really _____ . Now his parents' are _____ him .[ ]
A. disappointing; disappointed at
B. disappointed; disappointed about
C. disappointed; disappointing by
D. disappointing; disappointed with
A.mgtgθ
B.mgsinθ
C.μmg
D.μmg