For pumping the bilges，a 54 foot long “T-Boat”，which is not a ferry，but is certificated to carry 30 passengers，must be fitted with at least（）.

A.one fixed power pump and one portable hand pump

B.one fixed hand pump and one portable hand pump

C.two portable hand pumps

D.either "A" or "B"

压接式连接是利用管件凸缘内的橡胶圈来实施密封，主要适用于管径（）50mm以下的铜管的连接。

A.20mm

B.30mm

C.40mm

D.50mm