题目

下列说法正确的是：A.体积很小的物体，不一定可以看作质点B.“前6秒”指的是时间，而“第6秒”指的是时刻C.加速度为负值时，物体一定在做减速运动D.质点某时刻的速度为零，则该时刻的加速度也一定为零 答案：【答案】A【解析】A．体积很小的物体，不一定可以看作质点，而看自身大小对研究问题有无影响，故A正确；B．“前6秒”指的是时间，“第6秒”指的也是时间，选项B错误；C．加速度为负值时，当速度也为负值时，物体做加速运动，选项C错误；D．质点某时刻的速度为零，则该时刻的加速度不一定为零On Thursday afternoon Mrs. Clarke, dressed for going out, took her handbag with her money and her key in it, pulled the door behind her to lock it and went to the over 60s Club. She always went there on Thursdays. It was a nice outing for an old woman who lived alone.At six o’clock she came home, let herself in and at once smelt cigarette smoke. Cigarette smoke in her house? How? How? Had someone got in? She checked the back door and the windows. All were locked or fastened, as usual. There was no sign of forced entry.Over a cup of tea she wondered whether someone might have a key that fitted her front door — “a master key” perhaps. So she stayed at home the following Thursday. Nothing happened. Was anyone watching her movements? On the Thursday after that she went out at her usual time, dressed as usual, but she didn’t go to the club. Instead she took a short cut home again, letting herself in through her garden and the back door. She settled down to wait.It was just after four o’clock when the front door bell rang. Mrs. Clarke was making a cup of tea at the time. The bell rang again, and then she heard her letter-box being pushed open. With the kettle of boiling water in her hand, she moved quietly towards the front door. A long piece of wire appeared through the letter-box, and then a hand. The wire turned and caught around the handle on the door-lock. Mrs. Clarke raised the kettle and poured the water over the hand. There was a shout outside, and the skin seemed to drop off the fingers like a glove. The wire fell to the floor, the hand was pulled back, and Mrs. Clarke heard the sound of running feet1.Mrs. Clarke looked forward to Thursday because ______.A.she worked at a club on the dayB.she had visitors on ThursdayC.she visited a club on ThursdayD.a special visitor came on Thursday2.What does the expression “a master key” in Paragraph 3 most probably mean?A.A key to all the doorsB.A key only to the woman’s doorC.A key only its master can useD.A key not everyone can use3.On the third Thursday Mrs. Clarke went out ______.A.because she didn’t want to miss the club againB.to see if the thief was wandering outsideC.to the club but then changed her mindD.in an attempt to trick the thief4.The lock on the front door was one which ______.A.needed a piece of wire to open itB.could be opened from inside without a keyC.couldn’t be opened without a keyD.used a handle instead of a key