单项选择题
The domestic fresh water pump starters are controlled by pressure switches which operate when the pressure in the tank varies within predetermined limits as water is drawn offThe word “which” means （）.
A.starters B.pressure switches C.pressure D.water
单项选择题 In general, domestic flesh water tank kept under pressure by an external supply of （）.
单项选择题 The abbreviation "TDS" about the potable water probably means （）.
单项选择题 A condenser is a vessel in which（） is deprived of its latent heat of vaporization and so changed to its liquid state.
