假岩屑主要由滞后的岩屑和井壁垮后下来的岩石碎块组成。
参考答案：错
—May we leave the classroom now?
—No , you ____.You ____to leave until the bell rings.[ ]
A. mustn't; are allowed
B. don't have to ; are supposed
C. needn't; aren't allowed
D. can't ; aren't supposed
房屋价格的形成有三种方法：成本+利润，市场比较法，和（）。
