| Animals do many useful and entertaining
jobs. (38) {{U}}Dogs are particularly valuable in guiding the blind (a trained dog
can learn never to cross a busy street when cars are coming, even if his master
commands him to do so), protecting property, finding lost people, and hunting
criminals.{{/U}} Horses are used in guarding herds, carrying men in lands where
there are no roads, and helping farmers plow fields. Pigeons have long been used
to carry message. Wild animals from the jungles, forests and seas are very
popular performers in circuses and movies. People realize that, although animals
may not have the same intelligence as human beings, they are smart enough to
learn certain things. The first thing a dog is taught is to obey. It should not take too long for him to learn commands. Simple orders, such as "sit, lie down A. to obey all orders B. to obey only safe orders C. never to cross busy roads D. to cross roads when commanded [简答题]An ecosystem is a group of animals and plants living in a specific region and interacting with one another and with their physical environment．Ecosystems include physical and chemical components，such as soils，water，and nutrients that support the organisms living there．These organisms may range from large animals to microscopic bacteria．Ecosystems also can be thought of as the interactions among all organisms in a given area；For instance，one species may serve as food for another．People are part of the ecosystems where they live and work．Human activates can harm or destroy local ecosystems unless actions such as land development for housing or business are carefully planned to conserve and sustain the ecology of the area．
[单项选择]It is animals and plants which lived in or near water whose remains are most likely to be preserved, for one of the necessary conditions of preservation is quick burial, and it is only in the seas and rivers, and sometimes lakes, where mud and silt have been continually deposited, that bodies and the like can be rapidly covered over and preserved.
But even in the most favorable circumstances only a small fraction of the creatures that die are preserved in this way before decay sets in or, even more likely, before scavengers eat them. After all, all living creatures live by feeding on something else, whether it be plant or animal, dead or alive, and it is only by chance that such a fate is avoided. The remains of plants and animals that lived on land are much more rarely preserved, for there is seldom anything to cover them over. When you think of the innumerable birds that one sees flying about, not to mention the equally numerous small animals like field mice and voles which you A. a large number of remains B. a number of remains C. only a small number of remains D. few remains 我来回答: 提交
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