词汇	ring-down system
释义	ring-down system 振铃信号制
随便看	double-projection direct-viewing stereo-plotter double projection instrument double-projection plotter Double-projective double projector double promontory double promoted catalyst Double promoter double-pronged double-pronged attack double pronged tenaculum double prong guard double prongs forceps double prongs retractor double proofed fabric double proof standard double-prop double propellant Double Propellant Loading double-propeller plane double-propeller planes double propeller turbine engine double properties double-properties double-properties turbine disk