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问题 多项选择题

炮弹发射后在空中飞行，若不计空气阻力，下列说法中正确的是（）

A.炮弹只受重力作用，方向沿竖直方向向下

B.若炮弹的质量是m，则其重力大小为mg

C.炮弹在飞行中还受到一个冲力，其方向不断发生变化

D.炮弹在飞行过程中还受到大炮对它的推力作用，其方向不变

答案

参考答案：A, B

解析：炮弹发射后在空中飞行，若不计空气阻力，炮弹只受重力作用，因炮弹离开大炮，所以不存在大炮对炮弹的推力和冲力，A对，CD错；若炮弹的质量是m，则其重力大小为mg，B对。

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 (1) a job or advancing in one, the ability to read and comprehend (2) can mean the difference between success and failure. Yet the unfortunate fact is that most of us are (3) readers. Most of us develop poor reading (4) at an early age, and never get over them. The main deficiency (5) in the actual stuff of language itself—words. Taken individually, words have (6) meaning until they are strung together into phrases, sentences and paragraphs. (7) , however, the untrained reader does not read groups of words. He laboriously reads one word at a time, often regressing to (8) words or passages. Regression, the tendency to look back over (9) you have just read, is a common bad habit in reading. Another habit which (10) down the speed of reading is vocalization—sounding each word either orally or mentally as (11) reads.
To overcome these bad habits, some reading clinics use a device called an (12) , which moves a bar(or curtain) down the page at a predetermined speed. The bar is set at a slightly faster rate (13) the reader finds comfortable, in order to "stretch" him. The accelerator forces the reader to read fast, (14) word by word reading, regression and subvocalization practically impossible. At first (15) is sacrificed for speed. But when you learn to read ideas and concepts, you will not only read faster, (16) your comprehension will improve. Many people have found (17) reading skill drastically improved after some training. (18) Charlie Au, a business manager, for instance. His reading rate was a reasonably good 172words a minute (19) the training; now it is an excellent 1,378 words a minute. He is delighted that how he can (20) a lot more reading material in a short period of time.

A．lies
B．combines
C．touches
D．involves
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单项选择题 B1型题

五苓散组成中不含有的药物是（）

A.茯苓

B.猪苓

C.白术

D.阿胶

E.泽泻
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