关于外毒素的叙述下列哪项是错误的?
A. 脱毒可形成类毒素
B. 主要由革兰阳性菌产生
C. 毒性强,对组织器官有选择性毒害效应
D. 化学成分是蛋白质
E. 细胞壁成分,性质稳定,耐热
Which of the following statements contain incomplete plosion? _____
A. Enjoy it, please.
B. For example.
C. Tell her to do it.
D. I’m a big big girl.
( )在区间(a, b)内的连续函数既有最大值又有最小值.
A. 对
B. 错
型号为STC89C52RC 40-I-PDIP双列直插式DIP封装单片机具有( )个引脚
A. 20
B. 30
C. 40
D. 50