Most people around the world are right-handed. This also seems to be true in history. In 1799, scientists studied works of art made at different times from 1,500 B.C. to the 1950s. Most of the people shown in these works are right-handed, so the scientists guessed that right-handedness has always been common through history. Today, only about 10% to 15% of the world's population is left-handed.

Why are there more right-handed people than left-handed ones? Scientists now know that a person's two hands each have their own jobs. For most people, the left hand is used to find things or hold things. The right hand is used to work with things. This is because of the different work of the two sides of the brain. The right side of the brain, which makes a person's hands and eyes work together, controls the left hand. The left side of the brain, which controls the right hand, is the centre for thinking and doing problems. These findings show that more artists should be left-handed, and studies have found that left-handedness is twice as common among artists as among people in other jobs.

No one really knows what makes a person become right-handed instead of left-handed. Scientists have found that almost 40% of the people become left-handed because their main brain is damaged when they are born. However, this doesn't happen to everyone, so scientists guess there must be another reason why people become left-handed. One idea is that people usually get right-handed from their parents. If a person does not receive the gene (基因) for right-handedness, he / she may become either right-handed or left-handed according to the chance and the people they work or live with.

Though right-handedness is more common than left-handedness, people no longer think left-handed people are strange or unusual. A long time ago, left-handed children were made to use their right hands like other children, but today they don't have to.

Playing with apps on smart phones is very common among young people. Let's try some special apps and enjoy them.

    Many years ago, most of our earth was covered with blocks (块) of ice. These ice blocks were as tall as high buildings in modern cities. Most of the ice was in the northern part of the world. Then the ice blocks started to move south. Cold and rain came with the ice. Animals had to move. At last, the ice began to melt (融化). After half a million years, most of it melted. More than half of the earth became covered with water. The climate became much warmer. Things began to grow. The earth began to look the way in which it looks today.

    Do you know what makes lightning (闪电)? {#blank#}1{#/blank#}

    Lightning strikes happen when ice and water in clouds rub (摩擦) together, and cause atmospheric (大气层的) changes. When this happens, it creates a static charge (静电). Lightning can strike inside the cloud, between two clouds or between a cloud and the earth. {#blank#}2{#/blank#}

    Lightning can be very dangerous. Every year, lightning kills people because it can start big fires or because it reaches a temperature of 28,000℃. About 1,000 people are hit by lightning every year in the United States, and about 100 of them die as a result.

    {#blank#}3{#/blank#}Scientists think that there are more than three million lightning strikes every day in the world. An American man, Roy Sullivan, who worked in a park, survived from the most lightning strikes. {#blank#}4{#/blank#}And he keeps the highest world record.

    Lightning is sure not something to play with. When lightning strikes, it's best to stay inside a large building. {#blank#}5{#/blank#}Also, do not lie down on the ground, or the electricity may go through you and cause a heart problem.

    If you had billions of dollars, would you donate almost all of it to charity? Well, that's what Mark Zuckerburg, CEO and founder of Facebook, just said he would do.
    Zuckerburg and his wife Priscilla Chan promised to give 90% of their Facebook shares to society. Right now that is about $45 billion, and they plan to donate the money to things like science and education.
    Many billionaires have done similar things. Bill Gates, creator of Microsoft, made The Giving Pledge, an activity in which billionaires promise donate more than half of their wealth to charities. This started in 2010, and now 139 people from 15 countries joined it.
    But giving back and helping others isn't just for big billionaires. People like Zuckerberg, and Gates may have more to give, but people with less are doing it, too.
    Especially around the holidays, people want to do their part and give back to people who are less lucky than them. Schools may have food collections where people bring a few food items, and together they can make a big donation to places like homeless people's homes.
    People also host special events like concerts of runs to be creative while raising money. Regular people donate whatever they can to US charities like the United Way and the American Red Cross.
    Then these charities are able to help US communities in different ways like education, health and improving the lives of the poor. These individual donations come together to make a big difference.