题干

正常人体内的造血干细胞能分裂产生各种血细胞,在体外,在某些因素的诱导下,却可以分化为神经细胞和肝细胞。其根本原因是这些造血干细胞()

A:有旺盛的分裂能力

B:能合成神经细胞或肝细胞需要的蛋白质

C:还没有分化

D:具有与受精卵相同的全套遗传基因

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D

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    When I opened the box at my 12th birthday party, I couldn't believe my eyes. I had really gotten a mobile phone!

    As soon as I got to my school the next morning I 1off my phone and asked everyone for their2.

    It felt like I didn't even exist in that class any more. I wouldn't pay much attention to the teachers because I was too busy on my 3. Luckily I didn't get 4using it. I was pretty sure that the teacher didn't5that I stopped paying attention to her6a week later we took a test and I failed. To make matters 7, my mom had to sign the test.

    It was hard to show my mom the 8 . She was used to seeing As and Bs on my tests. Well, at last, I showed her and she couldn't 9it. She was angry.

    Weeks passed and my parents started to10the fact that I had a phone. They would say,“We have noticed that you never pay attention to us. It's like you have your own little 11now and we don't communicate as much with your phone.”

    I acted like they were wrong, but then I started to wonder if it was true that I was spending too much 12on the phone.

    A week later I tried 13 a whole day without a phone. I had so much 14because I was actually spending time with my family and paying attention to them. From that day, I had a different opinion towards phones.

    Phones really take you away from the rest of the world. I'm not saying that phones are15and not to use them, but you do have to spare some time to spend with your family. My phone took away time from my homework and from my family. I will keep using my phone, but I will have it under better control.