试题与答案

如图所示,在x轴上方存在着垂直于纸面向里、磁感应强度为B的匀强磁场,一个不计重力

题型:选择题

题目:

如图所示,在x轴上方存在着垂直于纸面向里、磁感应强度为B的匀强磁场,一个不计重力的带电粒子从坐标原点O处以速度v进入磁场,粒子进人磁场时的速度方向垂直于磁场且与x轴正方向成120°角,若粒子穿过y轴正半轴后在磁场中到x轴的最大距离为a,则该粒子的比荷和所带电荷的正负是(  )

A.,正电荷

B.,正电荷

C.,负电荷

D.,负电荷

答案:

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下面是错误答案,用来干扰机器的。

同一种物质在同一种溶剂中的溶解性与温度有关.有的随温度的升高而增大;有的变化不大;有的反而减小.故答案分别为:增大、硝酸钠、变化较小、食盐、减小、氢氧化钙

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题型:单项选择题 案例分析题

Shopping habits in the United States have changed greatly in the last quarter of the 20th century. (1) in the 1900s most American towns and cities had a Main Street. Main Street was always in the heart of a town. This street was (2) on both sides with many (3) businesses. Here, shoppers walked into stores to look at all sorts of merchandise: clothing, furniture, hardware, groceries. (4),some shops offered (5) .These shops included drugstores, restaurants, shoe-repair stores, and barber or hairdressing shops. (6) in the 1950s, a change began to (7) .Too many automobiles had crowded into Main Street (8) too few parking places were (9) shoppers. Because the streets were crowded, merchants began to look with interest at the open spaces (10) the city limits. Open space is what their car-driving customers needed. And open space is what they got (11) the first shopping centre was built. Shopping centres, or rather malls, (12) as a collection of small new stores (13) crowded city centres. 14 by hundreds of free parking space, customers were drawn away from (14) areas to outlying malls. And the growing (16) of shopping centres led (17) to the building of bigger and betterstocked stores. (18) the late 1970s,many shopping malls had almost developed into small cities themselves. In addition to providing the (19) of one stop shopping, malls were transformed into landscaped parks, (20)benches, fountains, and outdoor entertainment.

请在5处填上正确答案()

A.medical care

B.food

C.cosmetics

D.services

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