在泥岩形成的过程中生成的，能反映岩石形成环境的是（）。
A.石英
B.高岭石
C.海绿石
D.伊利石
参考答案：C
Both of his parents died of illness so he ______ support his family at the age of 14.[ ]
A. must
B. should
C. could
D. had to
为加快文件的传递，可采用( )。
A．跨级行文
B．多级行文
C．越级行文
D．直接行文
