目前高等级公路多采用( )作为反滤层。
A．粗粒土
B．土工布
C．砂砾土
D．砾石
参考答案：B
—Shall we meet __ the office at eight tomorrow morning?
—All right. [ ]
A. back
B. back of
C. in the front of
D. in front of
原核生物的．RNA聚合酶的核心酶是
A．α2ββ'B．α2ββ'σdC．α2βD．αβ2
