Mr. Black,

We're very gladly to have received your money and some reading materials. Thank you very much. We had been studying hard since we came back to school. Under the help of our teachers and classmates, we have made great progresses in our studies. So we often praised and encouraged by our teachers and parents. We have made up our minds to study hard than before to learn every subject good in order to be admitted to key universities in the future.We're looking forward to see you, but we have no chance to go to the Hangzhou ourselves. So we hope you can post us a photo of yours soon.

Best wishes,

Yours,

《软件工程标准分类法》(GB/T 15538—95)是______标准。

A．强制性标准

B．推荐性标准

C．强制性行业

D．推荐性行业