用卤烷进行N-烷基化时,如果卤原子相同时,则反应活性短链大于长链。
参考答案:对
--- Tommy, your mum has been out without glasses!
--- Well, take it easy. _______ she is back home for them.
A.It is long before that
B.It won’t be long since
C.It won’t be long before
D.It will be long before
亚砷酸的作用特点()
A.只失活牙髓,对其他组织无破坏
B.渗透性差,不会出根尖孔
C.封药时间5~7天
D.无自限性
E.用于乳恒牙的牙髓失活