题干

下列有关性染色体的叙述,正确的一项是(  )

①人类的性染色体有X染色体和Y染色体两种类型,X染色体比Y染色体大;

②Y染色体上有决定睾丸形成的基因,所以男人的一对性染色体是YY;

③性染色体上不但具有与性别有关的基因,而且还有许多控制其他性状的基因;

④性染色体只存在于生殖细胞中,体细胞没有性染色体的存在.

A:①③

B:②③

C:①③④

D:①②③④

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A

同类题2

根据短文理解,选择正确答案。

    It was a beautiful Sunday morning, and Maggie and I were returning from our walk through the woods. We were only a couple of blocks from home when I spotted a cell phone and a credit card sitting on the road. We took them home. We always find amazing things on the street and she looks upon them as a movable feast-a chicken wing here or a barbecue rib there.

    I found another cell phone a few years back, too, and called a number in its phone book. I explained the situation to the guy who answered. He said it was his sister's and that he'd come to pick it up, which he did.

    And that was that. No verbal thank-you, no written thank-you, no “here's a box of chocolates” thank-you.

    I didn't have time to call anyone on my latest found cell phone. I was pouring myself coffee when it started to vibrate(震动) and dance across the kitchen counter.

    “Who's this?” someone asked when I picked up.

    “Who's this?” I countered(反问.“Sarah?”

    She was surprised at my knowing her name until she realized her name was on the credit card. “Could you send them to me?” she asked.

    She lives in Arlington, which is 2 miles from my house.

    “Hmm, no, ”I replied, adding that I thought she could come to get them, and that if I wasn't at home, they would be in my mailbox.

    A day later, when I was out for a run, someone retrieved(取回) them. There wasn't even a piece of paper put in the mailbox with “Thanks” on it. In this age of e-mail and cell phone, there's really no excuse. Years ago, I found something more precious than a $100 bill on the street: a driver's license. I saw  that its owner lived a couple of blocks from me, so I called him up. He asked whether I could slip the license through his front door.

    “I guess I could, ”I replied.

    And that was that.