空气污染的危害

试验和实验到底有什么区别? Write sentences.Use the words in Exercise. drop by 和drop at 有什么区别?I dropped by my friend's house yesterday.可不可以用dropped at 什么牌子的等离子切割机好 等离子切割机哪个牌子的好（数控等离子切割机）我是做一些钣金下料,通风管道用的.补充：经过几个月多家对比之后是从济南锦鸿机械韩经理那买的,确实很好用,没出过问题,价格还便宜.这 The chameleon is____________than the snake The orange snake is shorter than the black snake.这句话的意思! CNC 加工中心的英文全称是什么? 实验和试验的区别/ 实验和试验的区别在哪? Complete the following sentences with the words given in their proper forms.. Complete the sentences with a suitable word from Exerise A. A对B做正功,那么B一定对A做负功吗? 电子由A→B做负功则电场线方向? 电子从A到B做什么功? 物体A对物体B做负功,物体A需要消耗能量吗 杆对A是和B是不是做了功做了什么功?质量为M的a,b两球固定在轻杆的两端,杆可绕点O在竖直面内无摩擦转动,两球到中点O的距离La大于Lb,将杆拉到水平时由静止释放,则A在下降的过程中A.杆对A不 the snake is longer than the 枪的动力都是弹簧发力吗? The brown snake is longer than the grey snake.这句话的意思 Rewrite the following sentences with the phrases or experssions given1,He paid high price for the beautiful house.(at a ...price)2,Fashion keeps changing all the time.(from time to time) Rewrite the following sentences with “It is ……that ……”.1)They say that Ken is very good at operating computers.2)They reported that the number of wild animals in Africa is decreasing.3)People believe that Tom will win the first prize.4)Th 斜靠墙壁的木棒,对地面的压力与重力的关系. Revise the following sentences with the given rhetorical devices.1.David’s beloved grandfather passed away last week.2.He looked at me with a sad look.3.Sorry,my pocket can’t afford such a pair of shoes.4.I never believe until then that any meal Rewrite the following sentences using the given connectives 例如：Joe is happy.Therefore he sings.[so]Joes is happy so he sings1.Mr Cheng is making a lot of money.Therefore he is buying a new home.[so]2.I am very hungry.I didn't eat breakfast.[bec 为什么做负功 The elephant is( ) than the zebra.A.smaller B.taller C.older 弹簧笔的工作原理弹簧笔是怎么做到按一下笔头出来,再按一下又缩回去的?那部分齿轮是怎么工作的?最好能详细点,最好有原理图,要是有工作原理视频就更好了 A is smaller than B.B is bigger than C but smaller than D.Is D bigger than 弹簧工作原理是什么?第一问：弹簧在加速/静止情况下有什么不同?附加：弹簧测力计左边加5N,右边加10N,弹簧测力计示数多少? 什么是小老鼠,比房子高?what is smaller than a mouse and taller than house 弹簧 原理一个弹簧,在左端施加10N方向相左的力,再右端施加10N向右的力,我觉得这两个力等大反向,弹簧应该静止啊,为什么还形变呢?