Many students signed up for the race in the sports meeting .A. 400-meter-longB. 400-meters

问题补充：

Many students signed up for the race in the sports meeting .

A. 400-meter-long

B. 400-meters-long

C. 400 meters long

D. 400 meter long

答案：

(答案→)A. 400-meter-long

B. 400-meters-long

C. 400 meters long

D. 400 meter long

解析：考查复合形容词构词法。如果在几个词之间有破折号，那么都应该使用单数形式，如100-meter relay race100米赛跑。故A正确。句意：很多学生都报名参加运动会400米赛跑。