何谓中和抗体？

根据汉语意思补上单词。

1. The boy is in the ______(电梯). He is going to the top of the building.

2. —What are you doing?

    —He invited me to his birthday party this Sunday. I want to write him a ______(感谢信).

3. His hobby is playing ______(曲棍球).

4. There are many ______ (婴儿) in the garden. They are playing happily.

5. He usually has lunch at ______(中午).

发电厂的某些线路竟然用昂贵的银来制做，为什么不用便宜的铁或者铝来做呢？

将一小球竖直向上抛出，小球到达最高点前的最后一秒和离开最高点后的第一秒时间内通过的路程分别为x₁和x₂，速度变化量的大小分别为△v₁和△v₂，假设小球所受空气阻力大小不变，则下列表述正确的是

A．x₁>x₂，△v₁<△v₂

B．x₁<x₂，△v₁>△v₂.

C．x₁<x₂，△v₁<△v₂

D．x₁>x₂，△v₁>△v₂.

程序员在没计的软件系统中插入了一段专门设计的代码，使得它在任何时候都可以绕开正常的登录认证过程，进入该软件系统。这种恶意软件的攻击方式称为

A．特洛依木马

B．后门陷阱

C．逻辑炸弹

D．僵尸网络

石油沥青的一般由什么组成？