单项选择题
Backfire flame arrestors are installed on（）.
A.fuel tanks B.spark plugs C.carburetors D.distributors
单项选择题 Automatic fire dampers in ventilation systems are operated by use of（）.
单项选择题 Automatic fire dampers in ventilation systems are operated by a（）.
单项选择题 According to the T-Boat regulations the reason for providing adequate ventilation for a battery storage area is to prevent（）.
