如图，在平面直角坐标系中，边长为6的正六边形ABCDEF的对称中心与原点O重合，点A在x轴上，点B在反比例函数 位于第一象限的图象上，则k的值为(    )

 逻辑推理是化学学习中常用的思维方法．下列推理正确的是（　　）

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有人刷牙时牙龈经常出血，他应该补充（　　）

    Many people like animals. So they keep(饲养) 1 as pets. Usually people like to keep dogs, cats, fishes and 2 animals as their pets. Many young people keep animals 3 they think these animals are 4. Some old people keep pets because 5children don't live 6 them and they 7 lonely (孤独的).

    Mr. Li is an old man. He is a pet doctor (医生). He is friendly to all people and their pets. People in the neighborhood love 8 very much. People usually call him "The Pet Doctor". When people's pets are sick(生病的), they often ask Mr. Li for 9. Mr. Li can always help the sick pets get well soon. So he is 10 popular in the neighborhood.