Passage #2         What most people think of memory is, in fact, five different categories of memory. Our capability to remember things from. the past, that is, years or days ago, depends on two categories of memory-remote memory and recent memory, respectively. Think back to last year's birthday-what did you do? If you can remember that, you are using your remote memory. On the other hand, if you can't remember what you ate for lunch yesterday, that is a problem with your recent memory. But there are also other situations in which we use our memories. When taking a test, we need to draw on our semantic memories, the sum of our acquired knowledge. Or if we want to remember to do or use something in the future, either minutes or days later, this uses our immediate and prospective memories, respectively. Have you ever tried to remember a phone number that you got from the operator, but then forgot it right after? That would be a faulty immediate memory. But if you can easily remember to meet your friend for lunch next week, it means that at least your prospective memory is in good working order.         Many people think that developing a bad memory is unavoidable as we get older, but this is actually not the case. Of our five kinds of memory, immediate, remote, and prospective (if added with cues like memos) do not degrade with age. But how can we prevent a diminishing of our semantic, recent, and unaided prospective memories? The secret seems to be activity. Studies have shown that a little mental activity, like learning new things or even doing crossword puzzles, goes a long way in positively affecting our memories. Regular physical activity appears to be able to make our memories better as well, possibly due to having a better blood supply to the brain. The one thing to void-at all costs, though, is stress. When we are stressed, ourbodies release a hormone called cortisol, which is harmful to our brain cells and thus our memories.
29. What is the main idea of this passage?
(A) Functions of brain chemicals.
(B) Tricks for recognizing things.
(C) How to stay active.
(D) Types of human memory.