问题 选择题

如图所示,AA1为固定在竖直方向上的钢环C的竖直直径,弹簧一端固定于A点,另一端与穿在C中的小光滑环B固定,若更换不同劲度系数的弹簧B都能在 AA1右侧静止,在这些条件下,C对B的弹力的方向和大小为:

A.大小和方向都不同

B.大小和方向都相同

C.大小相同,方向不同

D.方向相同,大小不同

答案

答案:C

单项选择题
单项选择题

For many people today, reading is no longer relaxation. To keep up their work they must read letters, reports, trade publications, interoffice communications, not to mention newspapers and magazines: a never-ending flood of words.
In (36) a job or advancing in one, the ability to read and comprehend (37) can mean the difference between success and failure. Yet the unfortunate fact is that most of us are (38) readers.
Most of us develop poor reading (39) at an early age, and never get over them. The main deficiency (40) in the actual stuff of language itself—words. Taken individually, words have (41) meaning until they are strung together into phrases, sentences and para-graphs. (42) , however, the untrained reader does not read groups of words. He laboriously reads one word at a time, often regressing to (43) words or passages.
Regression, the tendency to look back over (44) you have just read, is a common bad habit in reading. Another habit which (45) down the speed of reading is vocalization—sounding each word either orally or mentally as (46) reads. To overcome these bad habits, some reading clinics use a device called an (47) , which moves a bar (or curtain) down the page at a predetermined speed. The bar is set at a slightly faster rate (48) the reader finds comfortable, in order to "stretch" him.
The accelerator forces the reader to read fast, (49) word-by-word reading, regression and sub vocalization, practically impossible. At first (50) is sacrificed for speed. But when you learn to read ideas and concepts, you will not only read faster, (51) your comprehension will improve.
Many people have found (52) reading skill drastically improved after some training. (53) Charlce Au, a business manager, for instance, his reading rate was a reasonably good 172 words a minute (54) the training, now it is an excellent 1,378 words a minute. He is delighted that how he can (55) a lot more reading material in a short period of time.

[A] master[B] go over [C] present [D] get through