水泥粉煤灰砂浆和掺用外加剂砂浆的搅拌时间不得少于（）s。
A.90
B.120
C.150
D.180
参考答案：D
______是DNA上的一个具有特定遗传信息的片段．______和______组成染色体．
—Shall I tell your best friends what happened to you yesterday?
— they ask you. [ ]
A. Not if
B. Not unless
C. Not except
D. Not though
