烧天然气时,133L型调压阀入口处天然气供气压力要稳定在()。
(A)5psi
(B)10psi
(C)15psi
(D)20psi
参考答案:C
We were swimming in the lake _____ suddenly the storm started.
A.when
B.while
C.until
D.before
在信号机或轨道电路发生故障不能开放进站或接车进路信号机时,可采取()方式开放引导信号。