上海交大2013年考博英语试题及答案

上海交大2013年考博英语试题及答案

doc.guandang.net 2013-8-21 来源：本站原创 作者：佚名

考博士难吗？ 考博英语历年真题破译！ 考博时间汇总 考博招生简章汇总 2013年上海交大考博英语试题及部分答案

第一篇

There are desert plants which survive the dry season in the form of inactive seeds. There are also desert insects which survive as inactive larvae (幼虫). In addition, difficult as it is to believe, there are desert fish which can survive through years of drought (干旱) in the form of inactive eggs. These are the shrimps (小虾) that live in the Mojave Desert, an intensely dry region in the south-west of the United States where shade temperatures of over 50C are often recorded.

The eggs of the Mojave shrimps are the size and have the appearance of grains of sand. When sufficient spring rain falls to form a lake, once every two to five years, these eggs hatch (孵化). Then the water is soon filled with millions of tiny shrimps about a millimetre long which feed on tiny plant and animal organisms which also grow in the temporary desert lake. Within a week, the shrimps grow from their original 1 millimetre to a length of about 1.5 centimetres.

Throughout the time that the shrimps are rapidly maturing, the water in the lake equally rapidly evaporates. Therefore, for the shrimps it is a race against time. By the twelfth day, however, when they are about 3 centimetre long, hundreds of tiny eggs form on the underbodies of the females. Usually by this time, all that remains of the lake is a large, muddy patch of wet soil. On the thirteenth day and the next, during the final hours of their brief lives, the

shrimps lay their eggs in the mud. Then, having ensured that their species will survive, the shrimps die as the last of the water evaporates.

If sufficient rain falls the next year to form another lake, the eggs hatch, and once again the shrimps pass rapidly through their cycle of growth, adulthood, egg-laying, and death. Some years there is insufficient rain to form a lake: in this case, the eggs will remain dormant for another years, or even longer if necessary. Very, very occasionally, perhaps twice in a hundred years, sufficient rain falls to form a deep lake that lasts a month or more. In this case, the species passes through two cycles of growth, egg-laying, and death. Thus, on such occasions, the species multiplies considerably, which further ensures its survival.