题目

如图，风车的支杆OE垂直于桌面，风车中心O到桌面的距离OE为25cm，风车在风吹动下绕着中心O不停地转动，转动过程中，叶片端点A、B、C、D在同一圆O上，已知⊙O的半径为10cm.。 （1）风车在转动过程中，点为A到桌面的最远距离为_____cm，最近距离为_____cm； （2）风车在转动过程中，当∠AOE＝45°时，求点A到桌面的距离(结果保留根号)． （3）在风车转动一周的过程中，求点A相对于桌面的高度不超过20cm所经过的路径长(结果保留π)．It's easy to see how the sawfish got its name. These frightful creatures can grow to be more than 6 meters (nearly 20 feet) long. Their bodies are flat and winged, like underwater airplanes. And their noses are shaped like chainsaws. Sawfish are predators of the sea. When a sawfish is hungry, it waves its sharp-toothed snout through a school of fish. Then, it lifts its nose and uses its mouth to inhale the injured victims. Hardy populations of sawfish thrived in warm waters along coastlines around the world for thousands of years. Over the past 200 years, however, human actions have severely endangered sawfish. Threats include fishing nets that snag the huge animals, often by mistake. Compared with other fish, sawfish reproduce late in life and at slow rates. These traits make it hard for them to recover from over fishing. Some people collect sawfish snouts as trophies: One snout recently sold for nearly $1,600 on eBay. Shamans, or priests, in some Asian cultures, use the toothy snouts in ceremonies to repel demons and disease. And sawfish are also a delicacy. A growing demand in Asia for the animal's fins for a pricey soup has contributed to the fish's disappearance. New efforts now aim to revive sawfish populations. Beginning next month, an international agreement will provide protection for all seven of the world's sawfish species. "Until 1998, this fish had never been formally studied in the United States," says Tonya Wiley of the Mote Marine Laboratory in Sarasota, Fla. "We didn't know such basic things as where they live, what habitat they use, how often they reproduce, how many young fish they have." Through historical studies and field research, scientists have become aware of how much the fish's numbers have dwindled. Today, there may be 90 percent fewer sawfish than there used to be. Wiley estimates that only 3,000 to 6,000 sawfish remain in US waters. 72. Which of the following is the best title for the passage? A. Long Nose, Hopeful Future            B. The Mote Marine Laboratory C. Sawfish in US                               D. The Past of the Sawfish 73. The sawfish got its name because _____. A. It can grow to be more than 6 meters long B. Its body is flat and winged, like underwater airplanes C. Its nose is shaped like chainsaws D. It can be used as a saw to cut down the trees 74. The number of sawfish becomes smaller than before because ____. A. compared with other fish, sawfish reproduce early in life and at fast rates B. in some Asian cultures, the toothy snouts can be used in ceremonies to repel demons and disease C. sawfish are also smelly, which attracts people to kill them D. fishing nets that snag the huge animals, often on purpose kill them 75. From the passage we can learn that _____. A. scientists knew where they live, what habitat they use before 1998 B. scientists have become aware of how much the fish's numbers have dwindled until 1998 C. there may be 30,000 to 60,000 sawfish in the past D. there may be 90 percent more sawfish than there used to be