Dear Peter,

Thanks very much on inviting me to your birthday party on Sunday. I’d like very much come but I will had an examination on Monday morning. It is a very important exam but I can’t afford to fail it. I’ll spend all the whole weekend reading and prepare for it. So I’m really sorry that I won’t be able to come in this time. Hope you can understand. I’ll take this chance to wish you wonderful time on your birthday. Happy birthday, Peter, and many happy return of the day!

Yours,

Li Ming

金属洛氏硬度试验结果中，用硬度、符号HR和使用标尺字母表示的标尺是（）。

A.（A、B和C）标尺

B.（B、C和D）标尺

C.（B、D和E）标尺

D.（A、C和D）标尺