鉴别硫酸庆大霉素可选择
A．硫色素反应B．茚三酮反应C．双缩脲反应D．三氯化铁反应E．与亚硝基铁氰化钠的反应
参考答案：B
- _______ David and Vicky _____ married?
- For about three years.[ ]
A. How long were; have been
B. How long have; have been
C. How long have; been
D. How long did; get
何谓高频保护的通道余量？
