题干

动物和人体内具有分裂和分化能力的细胞称为干细胞。对下图的相关叙述,错误的是

A:a过程表示干细胞能自我更新

B:b、c过程表示干细胞具有分化能力

C:a、b、c过程中细胞的遗传信息表达情况不同

D:b过程形成的细胞直接组成器官,可供器官移植使用

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答案(点此获取答案解析)

D

同类题2

阅读理解

B

    Most of us have ever imagined the life on a desert island. We sometimes imagine a desert island to be a sort of paradise(天堂) where the sun always shines. “Ripe fruit falls from the trees and you are free to sit around without any work. This is really a beautiful picture, isn't it? However, the other side of the picture is quite the opposite. Life on a desert island is awful. You either starve to death or live like Robinson Crusoe, waiting for a boat which never comes.

    Perhaps there is some truth in both these pictures, but few of us have had the chance to find out. We can only experience it in the story like the following.

    Many years ago, two men spent five days on a coral island and they wished that they could stay there longer. They were driving a badly damaged boat from the Virgin Islands to Miami to have it repaired. During the journey, their boat began to sink(下沉). They quickly put food, matches, and cans of beer into a rubber dinghy(救生筏) and rowed for a few miles across the Caribbean until they arrived at a tiny coral island.

    There were hardly any trees on the island and there was no water, but this did not seem to be a problem. The men collected rainwater in the rubber dinghy. As they had brought a gun with them, they had plenty to eat. They caught lobster and fish every day, and they thought they lived just like a king. Five days later, a tank passed by and saved them. However, they felt sorry that they had to leave

同类题3

阅读下面选段,回答后面小题。

生命常常是如此之美

    每天下午,接上孩子之后,我都要带着他在街上溜达一圈。闲走的时候,看着闲景,说着闲话,我觉得这是上帝对我劳作一天的最好奖赏。

    每次我们走到文华路口,我就会停下来,和一个卖小菜的妇人聊上几句。这个妇人脸色黑红,发辫粗长,衣着俗艳,但是十分干净。她的小菜种类繁多,且价廉物美,所以常常是供不应求,我常在她这里买菜,所以彼此都相熟。因此每次路过,无论买不买菜,都要停下和她寒暄几句。

    客户多的时候,也帮她装装包,收收钱。她会细细地告诉我,今天哪几样菜卖得好,卤肉用了几个时辰,西兰花是从哪个菜市上买的,海带丝和豆腐卷怎样才能切得纤细如发,而香菇又得哪几样料配着才会又好吃又好看。听着她絮絮的温语,我就会感到一波波隐隐的暖流在心底盘旋。仿佛这样对我说话的,是我由来已久的一个亲人。

    那位妇人的笑容,如深秋的土地,自然而醇厚。

    一天夜里,我徒步去剧院看戏,散场时天落了小雨,便叫了一辆三轮车。那个车夫是个年近五十的白衣汉子,身材微胖。走到一半路程的时候,我忽然想起附近住着一位朋友,我已经很久没见到她了,很想上去聊聊。便让车夫停车,和他结账。

    “还没到呢。”他提醒说,大约以为我是个外乡人吧。

    “我临时想到这里看一位朋友。”我说。

    “时间长吗?我等你。”他说,“雨天不好叫车。”

    “不用。”我说。其实雨天三轮车的生意往往比较好,我怎么能耽误他挣钱呢?

    然而,半个小时后,我从朋友的住处出来,却发现他果真在等我。他的白衣在雨雾中如一团朦朦的云朵。

    那天,我要付给他双倍的车费,他却执意不肯:“反正拉别人也是拉,你这是桩拿稳了的生意,还省得我四处跑呢。”他笑道。我看见雨珠落在他的头发上,如凝结成团的点点月光。

    负责投送我所在的居民区邮件的邮递员是个很帅气的男孩子,看起来只有二十岁左右。染着头发,戴着项链,时髦得似乎让人不放心,其实他工作得很勤奋。每天下午三点多,他会准时来到这里,把邮件放在各家的邮箱里之后,再响亮地喊一声:“报纸到了!”

    “干嘛还要这么喊一声呢?是单位要求的吗?”一次,我问。他摇摇头,笑了:“喊一声,要是家里有人就可以听到,就能最及时地读到报纸和信件了。”

    后来,每次他喊过之后,只要我在家,我就会闻声而出,把邮件拿走。其实我并不是急于看,而是不想辜负他的这声喊。要知道,每家每户喊下去,他一天得喊上五六百声呢。他年轻的声音,好似铜钟与翠竹齐鸣的回响。

    生活中还有许多这样的人,都能给我这种难忘的感受。满面尘土的清洁工,打着扇子赶蚊蝇的水果小贩,双手油腻的修自行车师傅……只要看到他们,一种无缘由的亲切感就会漾遍全身。

    这些尘土一样卑微的人们,他们的身影出没在我的视线里,他们的精神沉淀在我的心灵里。他们常常让我感觉到这个平凡的世界其实是多么可爱,这个散淡的世界其实是那么默契,而看起来如草芥一样的生命种子,其实是那么坚韧和美丽。

    我知道,没有天堂,生活就是天堂,许多人在天堂里睡着,而我是一个醒了的天使。