北京市东城区民用电网改造完成后，某居民小区变压器输出端的交变电压瞬时值表达式为“

已知数列{a_n}的通项公式an=n2-3n-4(n∈N*)，则a₄等于（　　）

A．1

B．2

C．0

D．3

根据对话情景和内容，从对话后所给的选项中选出能填入每一空白处的最佳选项。选项中有两项为多余选项。（E 涂AB ,F涂 AC, G 涂 AD）

A : Hello,6674209.

B: Oh, Hello. Could I speak to Jannet,please?

A:  __小题1:__She isn’t here. Can I take a message ?

B: Yes, please .___ 小题2:__  Is that Mrs Brown?

A: __小题3:__ Hello ,Bill.

B: Thank you for asking me to Jannet’s party on Sunday evening .__ 小题4:__

A: I’m sorry to hear that .

B: I hope all of you will have a good time.

A: Thank you .__ 小题5:__

B: T hank you. Goodbye.

A．Yes, this is Jannet’s mother.

B．This is Bill here.

C．Hold on for a moment.

D．I’m afraid you can’t .E. I’ll give her the message.

F. I’m very sorry but I can’t come.

G. Please give her my best wishes.

简述水箱爆裂或漏水较大应采取的应急措施？

抗生素治疗牙周病的原则，不正确的一项是（）

A.牙周基础治疗效果不好的

B.急性感染的牙周疾病

C.用药前应清除菌斑、牙石

D.尽量使用广谱抗生素

E.尽量采用局部给药的途径

特殊素质