With the development of ________, various ________ come into being. [ ]

A. advertising; advertising

B. advertisement; advertisements

C. advertisements; advertising

D. advertising; advertisements

一台起重机将重5000N的货物提高2m，如果额外功是2500J，则起重机做的有用功是　　　　　J，该起重机的机械效率是　　　　　。