While listening to the concert the audience is required to remain and keep quiet.A. seat

问题补充：

While listening to the concert, the audience is required to remain and keep quiet.

A. seated

B. to be seated

C. seating

D. to seat

答案：

(答案→)A. seated

B. to be seated

C. seating

D. to seat

解析：考查形容词用法。形容词seated就坐；remain后面接形容词，seat是动词，意为：使…就坐；能容纳…；句意：在听音乐会的时候，观众本要求就坐在自己的位置上，保持安静。故A正确。