煤层按厚度将煤层分为3类(),(),()。
参考答案:薄煤层<1.3m;中厚煤层1.3~3.5m;厚煤层>3.5m
Tom went to work late the snowstorm.
A.because
B.for
C.because
D.because of
遇水膨胀橡胶