煤尘堆积指井下巷道中连续长度超过5m，厚度为2mm的煤尘。
参考答案：对
一 What are you doing now?
— I am writing to my cousin. He moved to America two weeks ago.
He must be ______ receiving my e-mail. [ ]
A. 1istening to
B. 1ooking forward to
C. hoping to
羚羊角的化学成分是：（）
A.角蛋白
B.卵磷脂
C.胆固醇
D.脂肪酸
E.碳酸钙
