线路大、中修后，无垫层的碎石道床，枕下清砟厚度不得小于（）。
A.200mm
B.300mm
C.350mm
D.400mm
参考答案：B
If you don’t know the new word, you’d better ＿＿.
A．look up a dictionary
B．look up an dictionary
C．look it up in a dictionary
D．look up it dictionary
