飞机上所有的金属组件采用搭铁的目的是：（）.A.使各组及结构之间等电位 B.增加各构

聚合物水泥砂浆饰面喷涂，为了避免接槎______，下班时应使______收头。

根据语境，用恰当的语言完成对话。

(Jim is talking with Kangkang about English learning.)

J-Jim K-Kangkang

J: Hello, Kangkang. (87) ___________________________________

K: I am reading a report about the droughts in the southwest of China.

    It's said all the living things there are short of water now.

J: (88) ________________________________

K: Me, too. Our environment is getting worse.

J: I think so. (89) _________________________________

K: We should plant more trees and prevent people cutting down too many trees.

J: And what's more, (90) ________________________________

    Because water is important too people, animals and plants.

K: You're right. Our school has set up a "Greener School" group. 

     (91) _______________________________

J: I'd love to. Let's do something useful from now on.

K: Great!

如图所示，重力为的物体在水平向左的恒力的作用下，静止在倾角为的固定光滑斜面上.下列关于物体对斜面压力的大小的表达式，正确的是（ ） 

A．

B．

C．

D．

小亮最近买了一种新型手电筒，它使用8个高亮度的白色LED，LED又称发光二极管，使用2节7号电池， 如图，小亮把两节电池安装在电池盒内，闭合开关却发现它们不亮，把电池调转一下后重新装回却亮了，上述现象说明：二极管具有                       的特性。

用一个远用矫正和一个近用矫正两个部分组成的镜片为（）。

A、近用镜片

B、远用镜片

C、渐变镜片

D、双焦点镜片