既能生津止渴，又能滋阴润燥的药物是：（）。

A.石膏

B.芦根

C.知母

D.葛根

E.决明子

Maintenance activities include ______.
①making enhancements to software products
②developing a new software product
③correcting problems
④adapting products to new environments

A．①②

B．①③④

C．②③④

D．①②③④