厂房建筑材料非燃烧体的耐火极限应不低于（）。
A.20分钟
B.0.5小时
C.1小时
D.1.5小时
参考答案：D
The visiting minister expressed his satisfaction with the talk, _________ that he had enjoyed his stay here.
A．having added
B．to add
C．adding
D．added
