Exercise may hold the key to youth, according to a study published on Monday which showed people who keep fit are up to nine years biologically younger than those who do not. The findings are the first to show in humans how keeping fit affects the ageing process.

The study of 2,40twins found that a sedentary（久坐的）lifestyle raises the risk of a range of problems from heart disease to cancer and appears to play a key role in the ageing process.

It all appears to boil down to（归结为）the length of structures called telomeres（染色体终 端）---which protect the DNA on the chromosomes（染色体）,the researchers from King's College London wrote in the Archives of Internal Medicine.

Many studies have shown telomeres get shorter over time, suggesting the cells are ageing or dying. The study, which extracted （提取）a DNA sample from their volunteers, found people who exercised more each week had longer telomeres.

Exercise lowers the risk of a range of problems such as heart disease, diabetes and cancer, the researchers said. “It is not just walking around the block. It is really working up a sweat." said Tim Spector, a genetic epidemiologist who led the study, in a telephone interview.

The study found people who exercised energetically 3 hours each week had longer telomeres and they were 9 years biologically younger than people who did under 15 minutes.

Spector's team, who also adjusted for body weight, smoking, economic status and physical activity at work, also said moderate（适度的）exercise for 1-2 hours each week provided a four- year advantage.

Studying twins also provided a unique opportunity to judge the effects of exercise on people with the same or similar genetic make-up. the researchers said.

The reason why exercise has this effect is not clear but the researchers said they believe physical activity somehow defends against the natural process called oxidative stress （氧化应激反应）.which damages and kills cells.

Dust storms don't just happen in the middle of the desert. They happen in any dry area where loose dirt can easily be picked up. The sand blown into the air by the wind usually falls back down to the ground after a few hours. Smaller bits of particles (微粒) stay in the air for a week or longer and can be blown thousands of miles away. Dust from the Sahara is always blown across the Atlantic and keeps travelling as far as Caribbean.

The scary thing about sandstorm is that they can spread over hundreds of miles and rise over 10,000 feet (305 meters). They also have wind speeds of at least 25 miles per hour (40km). Not strong enough to blow the feathers off a chicken but still something worth avoiding.

Don't be surprised if you suddenly see a dust storm heading your way. Dust storms usually arrive without warning and move in the form of a big wall of dust. The dust makes driving impossible. Often they only last for a few minutes but storms usually leave serious car accidents behind. If you are in a car during a dust storm, remind the driver to pull over and turn off the headlights.

In mild (轻微的) dust storms, it's still impossible to walk around although you wouldn't want to. You can't see anything because of the dust particles flying around. It's not just the dust you want to avoid. The wind carrying the dust will leave things as if they were just hit by a tornado. The best thing to do is find a safe place in a building.

Why are some people more motivated to handle difficult things? And is there a way to make doing difficult things easy? To answer the question, we need to look at this: dopamine(多巴胺). Dopamine gives us the motivation to get up and do stuff.

In fact, your brain develops priorities in large part based on how much dopamine it’s expecting to get. If an activity releases too little dopamine, you won’t have much motivation to do it. But if an activity releases a lot of dopamine, you’ll be motivated to repeat it, over and over. So which behavior releases dopamine? Any activity where you anticipate there’s a potential reward releases it.

And in today’s digital society, we are flooding our brains with unnaturally high amounts of dopamine on a daily basis, even if we don’t know it. Some examples of high dopamine behavior include: scrolling through social media websites, playing video games, etc.

And you might think, “So what? It won’t harm me in any way. But you’d be wrong. Whenever an imbalance occurs, our body adapts to it and those high levels of dopamine became your new routine. Thus you develop a dopamine tolerance. This can be harmful because the things that don’t give you as much dopamine don’t interest you any longer. That’s why people prefer playing video games or browsing the Internet, compared with studying or working.

But it is possible to make doing difficult things feel easier. Separate yourself from the unnaturally high amounts of dopamine, or at least expose yourself to it far less frequently. Only then will low dopamine activities become exciting again. That’s why you might want to limit your phone and computer usage.

We are all dopamine addicts. And that’s a good thing because dopamine motivates us to achieve our goals. But it’s up to you to decide where you are going to get your dopamine. Are you going to get it from things that don’t benefit you or from working on your long-term goals? The choice is yours.