题目

弹簧振子做简谐运动的振动图象如图所示，已知弹簧的劲度系数为20 N/cm，则    A．图中A点对应的时刻振子所受的弹力大小为5 N，方向指向x轴的正方向B．图中A点对应的时刻振子的速度方向指向x轴的正方向C．在0～4 s内振子做了1.75次全振动D．在0～4 s内振子通过的路程为3.5 cm，位移为0 答案：BBamboo flooring（竹地板）is a growing trend in home flooring and is also a great improvement to traditional hardwood floors．It is the most environmentally friendly kind of natural flooring that you can select for your home．It is also a renewable（可再生的）resource,is stronger than steel,and does not suffer from problems as a result of temperature changes．Bamboo is one of the fastest growing plants on earth,and only takes five years to grow to adult form．Bamboo is harvested every five years,and starts to re-grow immediately after being harvested．For this reason,bamboo is a kind of grass,not a tree．Bamboo is hollow（空心的）but very hard and can stand up to 50,000 pounds of pressure per square inch．Bamboo flooring has become very popular with its rich and beautiful golden earth colors．But it is important to shop around for a good-quality bamboo flooring product that contains no formaldehydes（甲醛）,which is said to be the best kind of bamboo flooring．Many brands use cheaper bamboo that may contain formaldehydes,and this can cause indoor air pollution problems as certain chemical materials in the bamboo slowly release their pollutants into the air．So,why should we turn to bamboo to save the enviroment?In fact,bamboo cannot save the environment directly,but it is an excellent replacement product for much of the hardwood species of trees that are being harvested in rainforests．Once harvested,if these hardwood trees do grow back,it can take up to 200 years!Rainforests are the lungs of our planet and they make a significant contribution to global oxygen production．By selecting bamoo flooring,you can reduce the demand for hardwood materials and help save the environment for future generations．Of course,everyone wants to buy good-quality bamboo flooring．The brands（品牌）from our shop are very high in quality and have received a lot of public praise．【小题1】Bamboo is a kind of grass because _______．A．it grows quicklyB．it isn’t as high as a treeC．it doesn’t grow in forestsD．it is hollow【小题2】What kind of bamboo flooring is best?A．The strongest kind．B．The most expensive kind．C．The kind that has a beautiful color．D．The kind that contains no formaldehydes．【小题3】How can bamboo make a contribution to the environment?A．It can directly improve the environment．B．It does not release formalddehydes at all．C．It can replace hardwood tree products．D．It can produce a lot of oxygen．【小题4】The author wrote this passage in order to _______．A．explain the importance of bamboo flooringB．tell us his or her own bamboo flooring brands are goodC．tell people to care more about the environmentD．discuss the history of hardwood flooring