The ship had 500 passengers .A. on boardB. on the boardC. on a boardD. on boards

问题补充：

The ship had 500 passengers .

A. on board

B. on the board

C. on a board

D. on boards

答案：

(答案→)A. on board

B. on the board

C. on a board

D. on boards

解析：可联系答.案.网客服索取。