题干

1958年,美国科学家斯图尔德应用植物组织培养技术,将二倍体胡萝卜韧皮部的一些细胞进行离体培养,最终发育成完整的新植株(见右图)。关于这一科学事实,下列叙述中错误的是(   )

①该实验证明了植物细胞具有全能性 ②此种生殖产生的后代有广泛的变异
③韧皮部细胞通过减数分裂增加数目 ④此种生殖产生的后代能保持亲本的性状

A:②

B:②③

C:②④

D:③④

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答案(点此获取答案解析)

B

同类题1

阅读下面短文,从短文后各题所给的四个选项(A、B、C和D)中,选出最佳选项。

The Value of an Hour

    It was Thanksgiving morning. In the crowded kitchen of my small home I was busy preparing the traditional Thanksgiving turkey1the doorbell rang. I opened the front door and saw two small children in2clothes and thin little sandals(凉鞋), staying together at the door on the top step.

    “Any old3, lady?” asked one of them.

    I was4. I wanted to say “no” until my eyes were5their sandals, which were wet with heavy snow.

    “6 and I'll make you a cup of hot cocoa.”

    They walked7and sat down at the table. Their wet sandals left marks upon the8. I served them cocoa and bread with jam to fight9the freezing cold outside.10 I went back to the kitchen and started again on my household budget for Thanksgiving Day.

    The silence in the front room struck me. I looked in. The girl held the empty cup in her hands, looking at it. The boy asked in a flat voice,“Lady, are you11?”

    I looked at my old sofa covers(沙发套). The girl put her cup back in its saucer(托盘)12 and said, “Your cups match your saucers.” Her voice was13with a need that no amount of food could

    supply. They left after that,14 their papers against the wind. They hadn't said “Thank you.” They didn't need to. They had15me that I had so much for which to be grateful. Plain blue china cups and saucers were16worth five pence. But they matched.

    I tasted the potatoes and the meat soup. Potatoes and brown meat soup, a roof over our heads, my man with a good steady job—these17,too.

    I moved the chairs back from the fire and18the living room. The muddy(沾上泥的)19 of small sandals were still wet upon my floor. Let them be for a while, I thought, just in case I should begin to20how rich I am.