题目

用20 N的水平力在水平地面上拉重60 N的物体时，物体恰能被拉动；物体运动后只需18 N的拉力即可使物体做匀速直线运动．该物体静止在水平地面上，若用15 N的水平力拉该物体，物体受到的摩擦力大小为________；若用30 N的水平力拉该物体，物体受到的摩擦力大小为________；物体与地面间的动摩擦因数为________．完型填空 　　Have you ever imagined that you could be cloned like Dolly the sheep in the not too distant future? 　　The news that a human embryo (胚胎) has been 1 cloned for the first time has caused mixed reactions (反映). 　　The 2 was carried out by scientists from the Advanced Cell Technology Inc (ACT), in Massachusetts, US. The group 3 the news on November 25. 　　“This is 4 human being. A clone is alive, it walks, it breathes,” said Jamie Grifo, 5 on the study of cloning at New York University School of Medicine. 　　“This is a set of cells in a lab that will be used to 6 someone's life. ” 　　Such research could lead to treatment for 7 such as heart diseases, AIDS and even cancer, 8 scientists. 　　Despite high hopes from other scientists, the news raised concerns immediately from religious and political leaders. Several 9 in the US do not allow human cloning. President George W. Bush also made it clear that he is 10  any type of human cloning. However, the scientists at ACT said they have no interest at present in 11 an early embryo into __12__. 　　Animals have been cloned repeatedly since Dolly the sheep 13 in 1997. And there were no real technical 14 to stand in the way of scientists making a cloned human embryo. 　　This time the research group used traditional cloning technology with a human 15 　　 16 it was given DNA from an adult cell, the egg began to __17__.__18__ it was stopped from becoming a baby--at a stage in which it was 19 a ball of cells. The 20 technology has been used to clone sheep, cattle and monkeys. (1) [　　] A. in failureB. never C. successfullyD. not (2) [　　] A. researchB. report C. worksD. task (3) [　　] A. made knownB. made C. saidD. had (4) [　　] A. a clonedB. a man-made C. aD. not a cloned (5) [　　] A. a workerB. a head C. an expertD. an assistant (6) [　　] A. saveB. rescue C. cureD. treat (7) [　　] A. patientsB. health C. diseasesD. things (8) [　　] A. according to B. including C. besides D. argued (9) [　　] A. countriesB. nations C. peoplesD. states (10) [　　] A. forB. against C. researching forD. praising (11) [　　] A. developing B. building C. inventing D. discovering (12) [　　] A. a babyB. a man C. a womanD. a white man (13) [　　] A. diedB. appeared C. turned upD. was no more (14) [　　] A. questionsB. affairs C. businessD. problems (15) [　　] A. eggB. bless C. meatD. cell (16) [　　] A. BeforeB. After C. WhileD. And (17) [　　] A. growB. die C. changeD. grow up (18) [　　] A. AndB. But C. HoweverD. Yet (19) [　　] A. yetB. still C. notD. no (20) [　　] A. differentB. usual C. ordinaryD. same