Ready to go to soccer practice? Tap (轻击) an app on your smart phone and get into the car that drives up—all by itself. Unlike human drivers, it never falls asleep, texts its friends, or eats a hamburger while driving. 

Self-driving cars already exist (存在). And these days many car companies are trying their best to make cars smarter—some cars can already avoid accidents or park themselves.

Luckily, Google has started building 100 self-driving cars without any human controls. Instead, computer programs drive the cars. They use sensor's (传感器) that "see" 600 feet in all directions to detect obstacles (探测障碍物). One woman who took a ride in one of Google's cars said, ""

Self-driving cars could make the world a better place by cutting down the number of cars people need and the amount of oil those cars use. The car that takes you to soccer practice could know to pick up two or three of your teammates on the way. 

But not everyone looks forward to a future with self-driving cars. Taxi drivers and truck drivers would lose their jobs.  What if dangerous people get into the cars' brains? They could cause accidents on purpose or stop the cars from going anywhere. Finally, many people love the experience of driving. 

What do you think? Will self-driving cars make the world a better place?

—Thanks for your advice. 

I invited Sally to my party because I didn't want her .

Carl went to Hong Kong by plane . 

—What brand of computer do you use? I want to buy one. 

—Yes, but I'd rather ____.

—Really? How come?

—Sorry, Dad!

I saw an old woman as people filled the train. As I watched the poor woman, I thought about the letters my mother wrote and how a piece of paper turned into a love litter when a person put his self into it. I would write the woman one, I decided. I could drop it at her feet. I started writing but when I looked up, the woman was gone. 

Back on the train, just a few days later, my plan became clear. I was going to leave the letter I wrote to the woman for someone else to find. Then I would put other love letters all over New York City. And you want to know why? Because it made me feel something. 

In the following months, I started my own site, MoreLoveLetters. com, encouraging others to write and leave letters in their own communities. 

About a year later, a woman wrote to me about her friend Briana, a single mother struggling (挣扎) to pay the bills (账单). I put Briana's story on the website, encouraging anyone who read it to mail me letters of encouragement for Briana. 

A week later, I felt disappointed as I walked into the post office and opened PO Box 2061. It was nearly empty. 

"Oh, Box 2061," said the man at the front of the post office. "You got too much mail, dear. We moved your mail to a bigger box.

I mailed the love letters to Briana, and a week later, I got a thank-you e-mail from Briana's friend. "Thanks for your love letters,"she wrote. ‘They show we're not alone and that we're not struggling for nothing. "

After such an amazing reply to Briana's story, I was encouraged to continue. I continued mailing letters to hundreds of people who didn't expect to get mail except bills that day.

Greg, try your best to get good grades and don't .