通常使用的商品校准品是（）
A.一级标准品
B.二级标准品
C.三级标准品
D.四级标准品
E.以上均不是
参考答案：C
— Mark, please don't play basketball on the road. It's very dangerous.
— _____. I am going home at once. [ ]
A. Have a great time
B. Sorry, I won't do that
C. I'd like to
D. OK, with pleasure
烂喉痧的病因是（），治疗以（）为原则。
