问题
单项选择题 A1/A2型题
关于DNA分子，说法错误的是（）。
A.DNA是具有遗传特性的物质
B.碱基G与C通过2对氢键配对
C.维持DNA二级结构的力主要是氢键和碱基堆积力
D.DNA中G+C含量高的区段较A+T含量高的区段稳定
E.DNA是极性分子
答案
参考答案：B
解析：碱基G与C通过3对氢键配对而碱基A与T通过2对氢键配对。
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关于DNA分子，说法错误的是（）。
A.DNA是具有遗传特性的物质
B.碱基G与C通过2对氢键配对
C.维持DNA二级结构的力主要是氢键和碱基堆积力
D.DNA中G+C含量高的区段较A+T含量高的区段稳定
E.DNA是极性分子
参考答案：B
解析：碱基G与C通过3对氢键配对而碱基A与T通过2对氢键配对。
When I was a child, I had an old neighbour named Dr. Gibbs. He didn’t look like any other doctor I’ve ever known. He never 11__ at us for playing in his yard. I remembered him as a kind and _12_ person When Dr. Gibbs didn’t work, he planted trees. His house covered an area of ten acres, and his life’s goal was to make it _ 13_ . He had some interesting _ 14 _ concerning planting. He belonged to the “No pains, no gains” __15 of plant growing. He never watered his new trees. Once I asked _16__, he said, “Watering plants will spoil them, and if you water them, each successive tree_ 17_ will grow weaker and weaker. So you have to make things 18__for them and weed out the weak ones.” So he never watered his trees. He would _19__a pine, and instead of _20__it every morning, he beat it with a rolled-up newspaper. I __21__ him why he did so, and he said it was to get the tree’s _22__. I planted a couple of trees a few _23__ ago. I carried water to them for a solid summer, sprayed them and prayed over them. Two years of careful tending has _24__ in trees that expect to be _25__ to hand and foot. Whenever a cold wind blows in, they tremble their branches. Dr. Gibbs passed away a _26__of years after I left home. Now and then, I walked by his house and looked at the trees. They’re _27__ now, big and healthy. Funny things about Dr. Gibbs’ trees. Hardship and difficulty seemed to benefit them _28__ comfort and ease never could. Life is tough, whether we want 29_ to be or not. Too many times we pray for ease, but that’s a prayer seldom met. What we need to do is to pray for 30_ that reach deep into the earth, so when the rains fall and the winds blow, we won’t be swept away.
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