单项选择题
Fusible-link fire dampers are operated by（）.
A.a break-glass and pull-cable system B.electrical controls on the bridge C.a mechanical arm outside the vent duct D.the heat of a fire melting the link
单项选择题 From your position you observe a rotating white and green light to the north. This light is most likely（）.
单项选择题 From which type of cloud can a tornado or waterspout develop?（）
单项选择题 Freeboard is measured from the upper edge of the（）.
