The bottom of the mast rests on a part of the keel called the mast（）.

A.prevent the boom from being raised too high
B.prevent the boom from swinging
C.support the boom when not in use
D.prevent the boom from being lowered

A.the three month period immediately following the certificate's anniversary date
B.the three month period immediately preceding the certificate's anniversary date
C.three months either way of the certificate's anniversary date
D.the three month period centered on the certificate's anniversary date

A.holding angle
B.fleet angle
C.fluke angle
D.shank angle