题目

下列有关人体细胞分化、凋亡以及癌变的叙述，正确的是A.细胞分化实质是基因的选择性表达，可增加细胞种类B.细胞衰老过程中细胞内所储存的遗传信息发生改变C.细胞癌变是原癌基因和抑癌基因选择性表达的结果D.清除血浆中抗原的特异性免疫中不存在细胞凋亡现象 答案：【答案】A【解析】1、细胞分化是指在个体发育中，由一个或一种细胞增殖产生的后代，在形态，结构和生理功能上发生稳定性差异的过程。2、衰老细胞的特征：（1）细胞内水分减少，细胞萎缩，体积变小，但细胞核体积增大，染色质固缩，染色加深；（2）细胞膜通透性功能改变，物质运输功能降低One August afternoon, Richard Allen dropped off his last passenger, Mrs. Carey. Lifting two grocery bags, he followed her across the yard and stood on the step of her house. Glancing up, he saw a large wasp（黄蜂）nest under the roof. Allen had heard that wasps can become more likely to sting（sting, stung, stung蜇）in summer. He mentioned this to Mrs. Carey, who had opened the door.“Oh, they don’t bother me,” she said lightly. “I go in and out all the time.”Anxiously, Allen looked at the nest again-to see the wasps flying straight at him. “Hurry!” he shouted to Mrs. Carey. “Get in!”She stepped quickly inside. Allen ran for his mini-bus. Too late; they were upon him. Just as he jumped aboard, half a dozen red spots showed on his arm, and he felt more on his back and shoulders.As he was driving down the road, Allen felt as if something was burning at the back of his neck, and the “fire” was spreading forward toward his face. An immediate anxiety took hold of him. Allen knew that stings could cause some persons to die. But he had been stung the previous summer and the after-effects soon passed. However, what he didn’t know was that the first sting had turned his body into a time bomb waiting for the next to set off an explosion.Miles from the nearest medical assistance, Allen began to feel his tongue thick and heavy and his heartbeat louder. Most frightening, he felt his breathing more and more difficult. He reached for the radio mike（话筒）,trying to call the mini-bus center, but his words were hardly understandable. Signals were also poor that far out. He knew a rescue team was on 24-hour duty at the Amherst Fire Department’s north station. So his best chance was to make a run for it.Rushing down the mountain, Allen tried not to panic, focusing his mind on each sharp turn. He was almost through the last of them when he felt sure he was going into shock（休克）.Just then he reached for the radio mike again.“Call fire station,” he shouted, concentrating to form the words. “Emergency. Bee sting. Emergency. There in ten minutes.”“Five-ten,” the center replied. Hold on, Allen thought. Keep your eyes open. Breathe. Keep awake.At last he reached the station. Two firemen ran out. Allen felt their hands grasp him before he hit the ground. You made it, he thought.【小题1】It is mentioned in the passage that wasps are more likely to attack when_____.A. there are huge noises　　B. strangers are approaching　　C. the hottest season comes aroundD the air is filled with food smell【小题2】Allen didn’t know that if stung by wasps again, he would______.A．have no after-effectsB．suffer from sharper painC．become more sensitiveD．surely lose his life【小题3】Allen failed at his first attempt to send his message to the mini-bus center because _______.A．he was in a state of shockB．his radio equipment was poorC．he was unable to speak clearlyD．no one was on duty【小题4】Which would be the best title for the passage？A．A Race Against DeathB．Wasps, Bloody KillersC．Allen, A Helpless DriverD．War Against Wasps