完形填空

    One summer, Aunt Betta and Uncle Bill invited me to travel with them back home to Pennsylvania. I had never been1Los Angeles and was eager to meet our relatives.

    Our first night, we drove through the desert, and then through roads cut through hills. The next day we went through the Rocky Mountains. It was2driving up long inclines（斜坡） with abrupt U-shape turns on the steep hillsides, then driving3slowly with great caution. Beyond Colorado, we drove through miles of 4, where I saw actual food being grown. I5some of the crops.

    In one small town we passed through, Aunt Betta decided I needed new6and took me to a country 7. I was used to8dresses and skirts. Now I had my first pair of jeans, a flannel shirt, shorts and a T-shirt. I loved them all.

    9 we reached our destination. Uncle Bill's aunt had a perfect little two-story house. The first thing I 10was a bed in a cute little room — for me! I looked forward to that. It would be like sleeping in a dollhouse. In the backyard, I saw red things11the back fence. Uncle Bill's uncle said, "I think you never ate a 12tomato in L.A." I hadn't. He 13picked one for me.

    I met all my new aunts, uncles and cousins. My cousins taught me how to do cartwheels (恻手翻) in the big front yard. Country people have more14, I thought.

    All the adults cried when we 15, but I took home all the 16of everything I'd seen. Back in L.A., my lungs hurt when I took a deep breath. I 17 the fresh air. I dreamed of homegrown tomatoes. My country clothes seemed out of 18, but I wore them anyway.

    I was two weeks late starting19, but I told my teachers only that I'd been in Pennsylvania and decided to 20all the rest to myself. If only they could have experienced everything that I did!

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CaliforniaCondor's Shocking Recovery

      California condors are North America's largest birds, with wing-length of up to 3 meters. In the 1980s, electrical lines and lead poisoning(铅中毒) nearly drove them to dying out. Now, electric shock training and medical treatment are helping to rescue these big birds.

      In the late 1980s, the last few condors were taken from the wild, and there are now more than 150 flying over California and nearby Arizona, Utah and Baja in Mexico.

      Electrical lines have been killing them off. “As they go in to rest for the night, they just don’t see the power lines,” says Bruce Rideout of San Diego Zoo. Their wings can bridge the gap between lines, resulting in electrocution(电死) if they touch two lines at once.

So scientists have come up with a shocking idea. Tall poles, placed in large training areas, teach the birds to stay clear of electrical lines by giving them a painful but undeadly electric shock. Before the training was introduced, 66% of set-freed condors died of electrocution. This has now dropped to 18%.

Lead poisonous has proved more difficult to deal with. When condors eat dead bodies of other animals containing lead, they absorb large quantities of lead. This affects their nervous systems and ability to produce baby birds, and can lead to kidney(肾) failures and death. So condors with high levels of lead are sent to Los Angeles Zoo, where they are treated with calcium EDTA, a chemical that removes lead from the blood over several days. This work is starting to pay off. The annual death rate for adult condors has dropped from 38% in 2000 to 5.4% in 2011.

        Rideout's team thinks that the California condors’ average survival time in the wild is now just under eight years. “Although these measures are not effective forever, they are vital for now,” he says. “They are truly good birds that are worth every effort we put into recovering them.”

氚是氢的一种同位素，氚原子含有1个质子和2个中子。下列示意图能正确表示氚原子结构的是（   ）