aboard, abroad, board, broad

　　aboard 在船(或飞机，车)上。如：I never went aboard a ship.

　　abroad 副词，在国外或海外。如：He often goes abroad.

　　board 为动词，上(船，飞机，车)。如：The passengers are boarding the plane now.

　　broad 为形容词，宽广的。如：He has very broad shoulders.