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    Sandra Bullock turned 51 last month. But because she looks exactly the same as she did in Miss Congeniality, a movie filmed back in the 20^th century, everyone calls her “ageless.” Bullock is just one of a number of stars in their 40s and 50s who've had birthdays recently but have not gotten older, unlike the rest of us in their age group. Take Halle Berry. One website put a photo of her 20 years ago next to one of the newly 49-year-old Berry and dared us to choose which was which. “This Is What 49 Looks Like,” it said. Seriously, if that's what 49 looks like, I must be 71.

    However, even a generation ago, famous faces evolved. Look at a picture of Grace Kelly at age 52 in the early 1980s. She looks like a beautiful middle-aged woman. Today she'd look old for her age.

    The goal now is to prevent aging while you are still young, using all the magical nonsurgical options medicine has to offer. Eventually these techniques will become less expensive, and ordinary people my daughter's age will have them. Already anti-aging is starting to be considered maintenance, like coloring your hair. My friends and I find ourselves openly debating techniques that we used to make fun of. Does fat-freezing work? How much time do you have to spend in the gym to keep the body of a 35-year-old after 50? It's all so exhausting. But members of the next generation have it tougher. They'll have to ask themselves whether they want to spend their youth trying not to get old. I've already seen “Sexy at 70” headlines. Will everyone be expected to go to their graves(坟墓) looking hot?

    I also have to wonder what else we are slowing along with age. How do you move on if you're working so hard to stay the same? And besides, if you've known the ache of watching a daughter pack up for college, you know you can't stop the clock.

    One afternoon, my son came home from school and asked me, “Are all people the same even if their skin color is different?” I thought for a moment, then I said, “I'll explain. Let's go to a fruit store first. I have something interesting to show you.”
At the store, I told him that we needed to buy apples. And we bought some red apples, green apples and yellow apples.
   After we got home, I told Adam, “It’s time to answer your question.” I put one of each type of apple on the table: first a red apple, followed by a green apple and then a yellow apple. Then I looked at Adam, who was sitting on the other side of the table.
   “Adam, people are just like apples. They come in different colors, shapes and sizes. See, some may not even look as delicious as others.” As I was talking, Adam was examining each one carefully.
   Then, I took each of the apples and peeled them, placing them back on the table, but in a different place.“OK, Adam, tell me which one is the red apple, the green apple and the yellow apple.”He said, “I can’t tell. They all look the same now.”“Take a bite(一口) of each one. See if that helps you tell which one is which.”He took big bites, and then a huge smile came across his face. “People are just like apples! They are all different, but if you take off the outside, they’re pretty much the same on the inside.”“Right,” I agreed. “Just like everyone has their own features but they are nearly the same.”
   He completely got it. I didn’t need to say or do anything else.
   Now, when I eat an apple, it tastes a little sweeter than before. What perfect fruit it is!

已知正方形ABCD的面积为9cm²，正方形EFGH的面积为16cm²，则两个正方形边长的相似比为____．