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Most teenagers in the United States try to make time for school, family and friends. But some choose bigger goals. Here are the stories of two American teens working to make a difference in the world.
At age 15, Winter Vinecki has already had more successes than most people have in their lifetime.
"I recently completed a marathon（马拉松）on all seven continents and became the youngest person in the world to do so. And, I was really doing this for my dad."
Doctors discovered Winter's father had prostate cancer（前列腺癌）when she was nine years old. Her father died 10 months later.
"When he was first found ill I immediately knew I had to do something to help him.That's when I formed Team Winter for prostate cancer research."
Through Team Winter, Winter Vinecki has raised almost 500, 000 dollars. She has taken prostate cancer education worldwide from Africa to Asia through foot races called marathons, on seven continents.
The other teen is Jack Andraka. He invented an inexpensive tool that can help find lung cancer, when he was 15 at the time.
"Without the Internet, I would have never been able to learn all these materials i needed for this project."
Jack is now 17 and seeking patents（专利）for his latest inventions. He has developed low-cost water quality machines. They help take away heavy metals and chemicals from water.
How did Winter make a difference in the world?