题干

水稻花药离体培养的单倍体幼苗,经秋水仙素处理后形成二倍体植株,如图是该过程中某时段细胞核DNA含量变化示意图.下列叙述错误的是(    )

A:d﹣e过程中细胞内发生了染色体数加倍

B:a﹣b过程中细胞有时含有2个染色体组

C:e点后细胞内各染色体组的基因组成相同

D:f﹣g过程中不会发生同源染色体分离

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答案(点此获取答案解析)

A

同类题2

完形填空

    There are purple clothes, purple handbags, purple bicycles, purple furniture, even purple computers! So purple is one of the most1colors today. But in the past, purple was a very expensive and unusual color. Let's take a look at the rich2of the color purple.

    Some scientists believe that the first plants to appear on Earth over 500 million years ago3looked purple, not green. Plants today are green because4use green chlorophyll (叶绿素) to produce energy.5these early plants probably used something called retinal, which is a dark purple color.

    During the time of the roman Empire (37 BC-476 AD), it was very6to make purple dye (染料). The dye came from sea snails (海螺) .But10.000 dead sea snails7you just one gram (克)of purple dye… as well as a very bad smell! This8purple dye was called Tyrian purple, and it was the preferred9of emperors.

    In 16th--century England, purple was10for the king's family members. Queen Elizabeth Is clothes were purple, but ordinary people were not allowed to11the color.

    In 1856. William Perkin, an 18-year-old12student, noticed something strange while doing an experiment (实验). The chemicals (化学药品) he used to clean his instruments13with the chemicals he used in his experiment and produced a bright purple color. This14Perkin to start a company using this chemical mixture to make purple dye. The dye was much15than sea snail dye. Thanks to Perkin, now anyone can afford to wear purple clothes.

同类题4

根据短文理解,选择正确答案。

    I wandered into the small store where I usually buy milk, when the store owner received a call from a customer. The customer and his wife had shopped there several months earlier. He noticed that his wife really liked one thing in the store, so he wanted to buy it as a surprise.

    But the customer was in Tennessee, far away from the store which was in Maine. What was more, he had been to the store several months earlier, and it was difficult to believe that the store owner would remember him, or what he was looking for.

    The store owner took a few close-up photos with her camera, and e-mailed them to the customer on the computer. The customer looked at the photos, and decided which one he wanted. They talked and discussed a price over the phone. She took care of the credit card transaction (交易) online, and promised the gift would be shipped out that afternoon.

    The store owner was really smart. She was willing to push herself to find new ways to make the transaction actually happen. And it did work. However, it was the first time she had ever done it.

    I was amazed that the store owner discovered a creative solution that could lead to a new way of doing business. I was impressed by what she did—so easily, but how difficult it is for many of us to make that leap(飞跃). I'm not just talking about technology, but about learning how to adapt to change. Most people hate or fear change unless they get to know exactly what change needs to be made. However, we should realize that challenge and opportunity go hand in hand.