单项选择题
Deficient oxygen content inside a chain locker can be detected with（）.
A.litmus paper B.combustible gas indicator C.oxygen breathing apparatus D.oxygen indicator
单项选择题 Deck beams on a ship are generally spaced at equal intervals and run（）.
单项选择题 Day-shapes must be displayed（）.
单项选择题 Daylight savings time is a form of zone time that adopts the time（）.
