按照《民用建筑可靠性鉴定标准》的规定，民用建筑可靠性鉴定，可分为( )鉴定。

A．安全性

B．适修性

C．实用性

D．正常使用性

E．危险性

Great as Newton was, many of his ideas_____today and are being modified by the work of scientists of our time.

A．are to challenge

B．have challenged

C．are challenging

D．have been challenged