单项选择题 The air reservoirs must have （） fitted to prevent rupture in the event of fire.

单项选择题 Before liquid can flow into a pump, the air in the suction line must be （） sufficiently to cause the liquid to flow into the suction chamber.

单项选择题 Generally speaking, suction heads require to be （） for high speed or large capacities than for low speed or small capacities.