题目

以下运动中机械能守恒的是(        ).【1.5】(A)物体沿斜面匀速下滑(B)物体从高处以g/3的加速度竖直下落(C)不计阻力,细绳一端拴一小球,使小球在竖直平面内作圆周运动(D)物体沿光滑的曲面滑下 答案：CDDo you like crocodiles (鳄鱼) ? Do you know anything about crocodiles? Crocodiles appeared about two hundred million years ago. They once lived on the earth together with dinosaurs.Crocodiles only live where it is wet and hot. They spent most of their time lying around in the mud (泥) or the rivers. The crocodiles’ long tails are used when the animals are swimming. It can be swung (摇摆) with great speed and force (武力). One blow will knock down a man or even a big animal at once. Crocodiles are very well protected against their enemies by the hard bone plates (骨板) which cover most of their bodies, but because of the way their neck are formed, they can only see in front of themselves. With their rows of terrible sharp teeth, they catch food, which may be a fish, an animal or even a careless man, and then hold it below the water until it drowns (淹死). Crocodiles lay their eggs and leave them under leaves or sand. Baby crocodiles have special sharp teeth with which to break their way out of the shells (壳) on their own. Crocodiles were once all over the world. But in the past 50 years, the number of crocodiles has gone down rapidly because of humans. The long-nosed crocodile is shy and because of this, the people of West Africa sometimes catch it for food. But more people hunt them for expensive crocodile leather. Now this kind of ancient animal has to depend on humans to live. Isn’t that terrible?Animal Crocodileliving habitsCrocodiles and dinosaurs once lived on the earth at the same 1.. Crocodiles can’t live in dry and 2. areas. They like lying around in the mud or the rivers．Crocodiles catch food with their terrible sharp teeth and then drown it.Crocodiles’ long tails are 3. and their hard bone plates keep them safe from enemies. reproductionCrocodiles lay their eggs and leave them under leaves or sand.Baby crocodiles break their way out of the shells by 4. with sharp teeth.present situationIn the past 50 years, the number of crocodiles has gone down rapidly. It’s 5. to stop hunting crocodiles at once. 1.time 2.cold 3.strong/powerful 4.themselves 5.necessary 【解析】试题分析：短文介绍了稀有保护动物鳄鱼的生活习性、身体特征、繁衍后代等情况，但是鳄鱼的数量却因为人类捕杀而迅速下降，呼吁人们停止捕杀鳄鱼的行为。 1.考查细节理解题。根据第一段结尾They once lived on the earth tog...