Challenging work that requires lots of analytical thinking，planning and other managerial skills might help your brain stay sharp as you age，a study published Wednesday in the journal Neurology suggests.

Researchers from the University of Leipzig in Germany gathered more than 1，000 retired workers who were over age 75 and assessed the volunteers' memory and thinking skills through a battery of tests. Then，for eight years，the scientists asked the same group to come back to the lab every 18 months to take the same sorts of tests.

Those who had held mentally stimulating(刺激)，demanding jobs before retirement tended to do the best on the tests. And they tended to lose cognitive(認知)function at a much slower rate than those with the least mentally challenging jobs. The results held true even after the scientists accounted for the participants' overall health status.

“This works just like physical exercise，” says Francisca Then，who led the study. “After a long run，you may feel like you're in pain，you may feel tired. But it makes you fit. After a long day at work-sure，you will feel tired，but it can help your brain stay healthy. ”

It's not just corporate jobs，or even paid work that can help keep your brain fit，Then points out. A waiter's job，for example，that requires multitasking，teamwork and decision-making could be just as stimulating as any high-level office work. And “running a family household requires high-level planning and coordinating(協調)，” she says. “You have to organize the activities of the children and take care of the bills and groceries.

Of course，our brains can decline as we grow older for lots of reasons-including other environmental influences or genetic factors. Still，continuing to challenge yourself mentally and keeping your mind busy can only help.

28. Why did the scientists ask the volunteers to take the tests? ( )

A. To assess their health status. B. To evaluate their work habits.

C. To analyze their personality. D. To measure their mental ability.

29. How does Francisca Then explain her findings in paragraph 4? ( )

A. By using an expert's words. B. By making a comparison.

C. By referring to another study. D. By introducing a concept.

30. Which of the following is the best title for the text? ( )

A. Retired Workers Can Pick Up New Skills

B. Old People Should Take Challenging Jobs

C. Your Tough Job Might Help Keep You Sharp

D. Cognitive Function May Decline As You Age