测量附着水平，正确距离是（） A.龈缘至袋底 B.牙颈部至袋底 C.龈缘至釉牙骨质界 发布时间：2017-08-08 10:58 │ 来源：www.tikuol.com 题型：单项选择题 问题： 测量附着水平，正确距离是（）A.龈缘至袋底B.牙颈部至袋底C.龈缘至釉牙骨质界D.釉牙骨质界至袋底E.牙颈部至釉牙骨质界
题型：单项选择题 阅读下面短文，根据短文内容。补全表格中所缺的信息。 Many kinds of birds live in the United States, but the number of the birds is becoming smaller every year. One of the leading reasons is the growing number of pet cats. By keeping your pet cats in your home, you can help give birds a better possible chance to live. Of the 90 million pet cats in this country, about two-thirds are allowed to go outside. It is said that these cats kill hundreds of millions of birds each year, as well as billions of small animals such as rabbits and field mice. They can also bring illness to the animals that live in people's yard (院子), further weakening the health of the natural populations. Allowing pet cats to go outside is not just bad for birds and wildlife, it's also bad for the cats themselves. Outdoor cats can get sick very easily. They are in danger from traffic and attacks (攻击) from other animals. In fact, outdoor cats usually don't live past the age of five, while indoor cats often live to be 17 or older. Keep your pet cat inside! If you raise a young cat, it's your duty to let it play inside. Problem The number of birds is becoming 1._________; at the same time,many pet cats are in 2.__________ from traffic and attacks from other animals.Reason for the problemPet cats are 3._________ to go outside freely. What to do People who 4._________ a young cat have the 5._________ to let it play inside. 查看答案
题型：单项选择题 小明用100N的力踢一个重5N的足球，球离脚后在水平草地上向前滚动了20m．在球滚动的过程中（ ）A．小明对足球做功2000JB．重力对足球做功100JC．小明对足球做功2100JD．小明和重力对足球做功都是0J 查看答案
题型：单项选择题 航天飞机以很高的速度绕地球飞行，宇航员能够离开航天飞机在太空中行走而不被甩掉的主要原因是( )。A．宇航员身上都有一根绳子与航天飞机相连B．他们身上都背着一个火箭助推器使他们的速度与航天飞机相同C．太空中没有阻力，他们在太空中仍然保持着与航天飞机相同的速度D．此种传闻不太可靠，人不可能在太空中行走 查看答案