问题
多项选择题
α螺旋结构中的碱基对主要是
A．腺嘌呤-胸腺嘧啶
B．胞嘧啶-鸟嘌呤
C．尿嘧啶-鸟嘌呤
D．腺嘌呤-尿嘧啶
答案
参考答案：A,B
解析：DNA双螺旋结构中的碱基对主要是A-T(腺嘌呤-胸腺嘧啶)及G-C(胞嘧啶-鸟嘌呤)。
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α螺旋结构中的碱基对主要是
A．腺嘌呤-胸腺嘧啶
B．胞嘧啶-鸟嘌呤
C．尿嘧啶-鸟嘌呤
D．腺嘌呤-尿嘧啶
参考答案：A,B
解析：DNA双螺旋结构中的碱基对主要是A-T(腺嘌呤-胸腺嘧啶)及G-C(胞嘧啶-鸟嘌呤)。
阅读下面短文，掌握其大意，然后从16-35各题所给的A、B、C、D四个选项中，选出最佳选项。 She always wore a flower in her hair．Mostly I thought it looked 16 ．A flower to work? But no one questioned the young woman why a flower _17 her to work each day．In fact, we probably would have been more curious if she had 18 without it． She did so one day _19 she delivered a project to my office．“I _20 there is no flower in your hair today," I said _21 ．"I'm so used to seeing you wear one _22 it almost seems as if something is _23．” “Oh, yes," she replied quietly, in a rather sad voice．This was far from her _24_ bright personality．I knew l had questioned something _25 than a lost flower． “Today is the anniversary of my mother's death．I__26 her so much that I'm very sad．When I was a little girl, my mother would often _27_ flowers in my hair．But when I was 15 she died of cancer．I've just always worn a flower in my hair since then and _28 made me feel as though she__29 with me．Today, however, I think she would like a 30 that I am becoming self-dependent, after ten years of her death．And it seems that it is the flower that has to__31 ．” She met my eyes and then smiled sadly．“I needn't wear a flower to be _32 of her．It was just an outward sign of my treasured _33 they're still there even with the flower gone…Oh, here's the 34 I hope it meets with your agreement．" She _35 me the neatly prepared document, signed with a hand-drawn flower below her name．
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