【名词&注释】
有毒气体(toxic gas)、输尿管(ureter)、救生艇(boat)、防毒面具、驾驶台(driving platform)、救生衣(life jacket)、空气呼吸器(compressed air breathing apparatus)
[单选题]If the engine does start on air, but combustion does not immediately begin, the cause may be _____.
A. failure of the fuel pumps
B. starting air pressure too low
C. stop valve in air line closed
D. the turning gear still engaged