It took us ____ to finish the new work.

A. three hour and a half     B. three and a half hour    C. three and a half hours

抹灰饰面工程应严格控制外墙、柱、梁干湿度，事先应（），确保灰浆与基底牢固黏结，防止空鼓、裂缝等质量通病。