Although many factors affect human health during periods in space, weightlessness is the dominant and single most important one. The direct and indirect effects of weightlessness lead to a series of related responses. Ultimately, the whole body, from bones to brain, kidneys to bowels, reacts.
When space travelers grasp the wall of their spacecraft and jerk their bodies back and forth, they say it feels as though they are stationary and the spacecraft is moving. The reason is based in our reliance on gravity to perceive our surroundings.
The continuous and universal nature of gravity removes it from our daily notice, but our bodies never forget. Whether we realize it or not, we have evolved a large number of silent, automatic reactions to cope with the constant stress of living in a downward-pulling world. Only when we decrease or increase the effective force of gravity on our bodies do our minds perceive it.
Our senses provide accurate information about th
A. many factors
B. the dominant and single movement
C. jerking the bodies back and forth
D. losing the dependence of gravity
| There are four basic types of
competition in business that form a continuum from pure competition through
monopolistic competition and oligopoly (商品供应垄断) to monopoly. At one end of the
continuum, pure competition results when every company has a similar product.
Companies that deal in commodities such as wheat or corn are often involved in
pure competition. In pure competition, it is often the ease and efficiency of
distribution that influences purchase. In contrast, in monopolistic competition, several companies may compete for the sale of items that may be substituted. The classic example of monopolistic competition is coffee and tea. If the price of one is perceived as too high, consumers may begin to purchase the other. Coupons and other discounts (折扣) are often used as part of a marketing strategy to influence sales. Olig A. permitted B. reserved C. criticized D. devised [单项选择]Passage Two
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