由仅识别一种抗原表位的B细胞克隆产生的抗体是（）。
A.多克隆抗体
B.单克隆抗体
C.精提纯抗体
D.以上都是
E.以上都不是
参考答案：B
应急情况报告的基本原则是（）、准确、直报、续报。
I just don’t understand ________ that prevents so many children at school from being as happy as one
might expect.[ ]
A. what it is
B. what it does
C. what is it
D. why is it
