Sitting at the corner of the meeting room, he looked sad because there were so many problems __...

Sitting at the corner of the meeting room, he looked sad because there were so many problems __...

C

选C　考查非谓语动词。句意：坐在会议室的角落里，他看起来很伤心，因为仍然有许多问题需要解决。remain在there be结构中作后置定语，由于remain是不及物动词，故应用现在分词remaining；且settle与problems之间构成动宾关系，故用动词不定式的被动形式。remain之后接动词不定式表示动作还未完成。