垫碴起道时，垫碴作业每撬长度不得超过（）根轨枕，并随垫随填，夯实道床。
A、5
B、8
C、10
D、6
参考答案：D
It is reported that the United States uses_________ energy as the whole of Europe.
A．twice as
B．twice as much
C．twice as many
D．much twice as
关于艾滋病的诊断要素中，最有意义的是（）
A.高危人群
B.临床表现
C.抗HIV抗体
D.CD4+／CD8+T淋巴细胞比值
E.机会性感染
