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问题 单项选择题

种子经营者按照经营许可证规定的有效区域设立分支机构的，可以不再办理种子经营许可证，但应当在办理或者变更营业执照后（）日内，向当地农业、林业行政主管部门和原发证机关备案。

A、15

B、20

C、30

D、45

答案

参考答案：A

判断题

真寒假热证的表现有四肢厥冷、小便清长、下利清谷、口渴喜热饮等。
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单项选择题

The sun today is a yellow dwarf star. It is fueled by thermonuclear reactions near its center that convert hydrogen to helium. The sun has existed in its present state for about 4 billion, 600 million years and is thousands of times larger than the Earth.
By studying other stars, astronomers can predict what the rest of the sun’s life will be like. About 5 billion years from now, the core of the sun will shrink and become hotter. The surface temperature will fail. The higher temperature of the center will increase the rate of thermonuclear reactions. The outer regions of the sun will expand approximately 35 million miles, about the distance to mercury, which is the closest planet to the sun. The sun will then be a red giant star. Temperatures on the earth will become too hot for life to exist.
Once the sun has used up its thermonuclear energy as a red giant, it will begin to shrink. After it shrinks to the size of the earth, it will become a white dwarf star. The sun may throw off huge amounts of gases in violent eruptions called nova explosions as it changes from a red giant to a white dwarf.
After billions of years as a white dwarf, the Sun will have used up all its fuel and will have lost its heat. Such a star is called a black dwarf. After the Sun has become a black dwarf, the earth will be dark and cold. If any atmosphere remains there, it will have frozen onto the earth’s surface.

The word "there" underlined in Paragraph 4 refers to ______ .

A．our own planet

B．the outer surface of the sun
C．the core of a black dwarf

D．the planet mercury
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