牙髓失活剂使用不当，可引起（）。 A.弥散性硬化性骨髓炎 B.颌骨化学性坏死 C.牙

运动会100m决赛的时候，同学们测量了运动员到达距起跑点20m和100m处所用的时间，其中刘小磊的时间是3．4s和12．4s，周大伟的时间是3．6s和12．8s。请算出这两名运动员分别在0一20m和0一100m路程内的平均速度（计算结果保留一位小数）。

I stood up to speak and my mind went blank .Has this ever happened to you? You may be nervous in front of an audience（观众）.You may be worried that you didn’t prepare enough, You may have forgotten some of your facts. What can you do? Sometimes people prepare too much and become terrified if they can’t remember the words they have practised. It is a good idea to bring some notes to help you organize, but don’t memorize your speech. If you “go blank”,begin by explaining the purpose of your speech, and the test will probably follow.

小题1: “Go blank” here means       

A．to be absent-minded

B．to think too much suddenly

C．to be afraid of the audience

D．not knowing what to say at the moment小题2: Before the listeners, the speakers who have pre-pared enough    

A．never go bland

B．never feel afraid

C．may forget the prepared words

D．may forget the opening speech小题3:A good way to make to made a good speech is      

A．to memorize the speech

B．to organize the audience well

C．to have some brief motes at hand

D．to have the audience take notes小题4:The man who goes blank in front of the listeners should      .

A．begin with the purpose of his speech

B．cut off the rest of his speech

C．see his notes right away

D．find some way to draw the audience’s attention

CRH380A型动车组牵引控制为（）控制方式。

A.VVVF

B.VVFF

C.VFFF

D.FFVV

低压熔断器按结构形式不同，有触刀式、螺栓连接、圆筒帽、螺旋式、圆管式、瓷插式等形式。按用途不同可分为一般工业用熔断器、半导体保护用熔断器和自复式熔断器等。

砌筑砂浆用料水泥，选用同品种水泥的标号一般为砂浆的标号4～5倍为宜。