各种蛋白质的含氮量平均约为()
A.8%
B.12%
C.16%
D.20%
E.24%
参考答案:C
解析:氮是蛋白质的特征元素,各种蛋白质的含氮量很接近,平均为16%。
I ______ her present but didn't ______ it.[ ]
A. accepted; receive
B. received; receive
C. received; accept
D. accepted; accept
加热试管内物质时,管口应朝向自己,以便看清楚反应过程。