翻译下列句子,并将答案写在作业本上,周三上课讲评: 1. Research have established that when people are mentally engaged, biochemical changes occur in the brain that allow it to act more effectively in cognitive areas such as attention and memory. 2. And someone with a history of doing more rather than less will go into old age more cognitively sound than someone who has not had an active mind. 3. Too often we believe what accounts for others’ success is some special secret or lucky break. But rarely is success so mysterious. 4. The latter ignores the higher cost of providing full services to a scattered community and the cost in both money and time of the journeys to work for the suburban resident. 5. For the population as a whole, we must be more concerned with the delayed effects of absorbing small amounts of the pesticides that invisibly pollute our world.