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问题 单项选择题 A1/A2型题

某急性淋巴细胞白血病患者，通过化疗已进入缓解期。护士夜间巡视时，发现患者突然出现烦躁不安、剧烈头痛、呕吐、颈项强直，目前高度怀疑发生了中枢神经系统白血病。患者缓解期发生中枢神经系统白血病的主要原因是（）

A.免疫功能低下

B.多数化疗药不能通过血脑屏障

C.疗程不够

D.化疗药剂量不足

E.对化疗药产生耐药性

答案

参考答案：B

解析：中枢神经系统白血病(CNSL)系白血病细胞浸润脑膜和中枢神经系统引起。临床表现为头痛、头晕、呕吐、颈强直，严重者甚至抽搐、昏迷，患者脑脊液压力增高。CNSL多发生在缓解期，以急性淋巴细胞白血病最多见，儿童尤甚。由于化学药物难以通过血脑屏障，隐藏在中枢神经系统的白血病细胞不能有效地被杀灭，因而引起CNSL。

填空题

半抗原具有免疫反应性，而无免疫原性，半抗原与载体结合后成为完全抗原，具有（）性。
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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.

What is the primary purpose of this passage

A．To alert people to the dangers posed by the sun.
B．To discuss conditions on earth in the far future.
C．To present a theory about red giant stars.
D．To describe changes that the sun will go through.
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