30. 下列中那一組掛旗可表示「世界協調時（UTC）0820」？ (A)T0820 (B)G0820 (C) Z0820 (D) W0820

17. Your vessel was vibrated heavily at a range of numbers of revolutions of the engines because synchronization occurs between the periods of a vibration of the hull and those caused by the inertia of the reciprocating parts of engines. What do we call this speed? (A)Regulative speed. (B)Critical speed. (C)Calibrating speed. (D)Difficult speed.