Dinosaurs died out long before people appeared. Dinosaurs lived from about 230 million years ago to about 65 million years ago. There are several theories about why dinosaurs became extinct. Many scientists believe that there was a sudden, (22) _____ event. They think that an asteroid or comet (23) _____ with the earth. Fire from the impact burned large areas. Dust blocked sunlight from (24) _____ the surface of the earth. Acid rain fell everywhere. Plants could not grow. There was no food for the plant-eating dinosaurs, so they died out. Other scientists think that the environment changed. Maybe the (25) _____ grew colder and dinosaurs slowly became extinct over several million years. Many scientists think that birds descended from a small kind of dinosaur. If this is true, then dinosaurs are still (26) _____ in the form of modern birds. 22. A. violet B. violence C. violent D. violently 23. A. crashed B. collided C. confronted D. met 24. A. reaching B. arriving C. approaching D. coming 25. A. days B. atmosphere C. weather D. climate 26. A. lively B. alive C. living D. live