题干

孟德尔的一对相对性状的遗传实验中,具有1:1比例的有(    )

①子一代产生的不同类型配子的比例    ②子二代的性状分离比

③子一代测交后代性状分离比 ④子一代产生的雌、雄配子比例

⑤子一代产生的不同类型的雌配子比例  ⑥子一代产生的不同类型的雄配子比例

A:①②④⑤⑥

B:①③⑤⑥

C:①③④⑤

D:①③④⑥

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B

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    Ben, at the age of 23 ,was the youngest man to ski solo to the North Pole. He dragged a 180-kilogramme sledge (雪橇) over 1,420 miles through the worst Arctic conditions. This year, Ben plans to ski solo from the Antarctic coast to the South Pole and back in the autumn, carrying all his supplies on his sledge.

    Ben Saunders was fired after persuading the firm to support his disorganized first adventure. “Everything that could go wrong did go wrong. We didn't get to the Pole, so we had no media interest. No one heard about it.”

    “People said it was impossible for me to get to the Pole. I said, “No, I can get there,” and I did. Self-belief, I see it as being a bit like a muscle — it's my belief that the more you stretch yourself the stronger it gets. If you never do anything that's uncomfortable or risky then your self-belief gets weaker. So that's one of the lessons I've figured out along the way.

    “My Antarctic adventure is just practicable and that's what is exciting to me. If I knew I could do it without too much bother, I wouldn't be interested." Why? “Personally I'm attracted by the human performance element to it. Not that long ago, running a marathon was seen as the top point of human attempt, and now I wouldn't be that surprised if my mum said she was going to run one."

    People's horizons are changing. “I'm not particularly gifted. I've just chosen this one goal to achieve and I've been working hard to realize it. And that's the thing that attracts me: with enough training and enough determination, enough focus and preparation, how far can we go? And I dont think I've found out yet.”