母差保护范围是从母线至线路（）之间设备。

Should students make friends on line?some people think the Internet help make 1.______

many friends .Chatting online ,students can express his feelings          2.______

and opinions more freely ,and even get help at their foreign 3.______

language studies Others ,therefore ,think students should not . 4.______

They say making friends online is waste of time , 5.______  

which should be spent more meaningfully on study . 6.______

Besides ,some students get cheat on line .   7.______

It is my opinion whether students should place their study，8.______

health and safe before other things . 9.______

After all ,we can find friend in our classmates.. 10.______

填入下面横线处的句子，排列顺序最恰当的一项是（   ）（2分）

进入天山，戈壁滩上的炎暑就远远地被撇在后边，迎面送来的雪山寒气，立刻会使你感到像秋天似的凉爽。             。当这个时候，饮马溪边，你坐在马鞍上，就可以俯视那阳光透射到的清澈的水底，在五彩斑斓的水石间，鱼群闪闪的磷光映着雪水清流，给寂静的天山添上了无限的生机。

①蓝天衬着高矗的巨大的雪峰，在太阳下，几块白云在雪峰间投下云影，就像白缎上绣上了几朵银灰的暗花。

②这飞泻下来的雪水，在山脚汇成冲激的溪流，浪花往上抛，形成千万朵盛开的白莲。

③那融化的雪水，从峭壁断崖上飞泻下来，像千百条闪耀的银链。

④可是每到水势缓慢的洄水涡，却有鱼儿在跳跃。

A．①③②④

B．①②③④

C．②③①④

D．③②④①

在下列关系运算中，不改变关系表中的属性个数但能减少元组个数的是( )。

A) 并
B) 交
C) 投影 D) 除

叙述水解FV-40的联锁动作原理。