煤粒中大于80mm的矸石的质量分数称之含矸率。
参考答案：错
由1，2，3，4，5，6组成没有重复数字且1，3不相邻的六位偶数的个数是__________.
He will spend six hours at his desk _______ he finishes his composition.
A．before
B．until
C．after
D．when
