What do the couple learn from their experience?

Suppose you are Doctor Bob, please write a reply to Alice. (假定你是Bob医生, 请根据左列Alice的来信写一封至少100词的回信) （注意：短文中不得出现考生的中文姓名及其他相关信息，否则不予评分。）

The best title of the passage is ___________.

From a dam, people can use the water for ___________.

The water in the river is polluted because of _____________.

Rivers are one of our most important natural resources (资源). Many of the world's great cities are located(坐落) on rivers, and almost every country has at least one river running through it that plays an important role in the lives of its people.

 Since the beginning of the history, people have used rivers for transportation(运输). The longest one in the United States is the Mississippi. The lifeline of Egypt is the Nile. To the people of India, the Gangs is great, but it is also important for transportation; Ships can travel along it for a thousand miles. Other great rivers are the Congo in Africa and the Mekong in southeast Asia. The greatest of all for navigation (航海), however, is the Amazon in Brazil. It is so wide and so deep that large ships can go about two thousand miles upon it.

  Besides transportation, rivers give food, water to drink, water for crops(庄稼), and chances for fun and entertainment for the people who live along their banks. In order to increase(增加) the supply of crops, engineers sometimes build a dam (大坝) across a river and let a lake from behind the dam. Then people can use the water not only to irrigate (灌溉) their fields but also to make electricity for their homes and industries.

  However, large cities and industries that are located upon rivers often make problems. As the cities grow in size and industries increase in number, the water in the rivers becomes polluted with chemicals(化学物质) and other materials. People are learning the importance, however, of doing more to keep their rivers clean if they want to enjoy the benefits (利益) of this natural resource.

The greatest river for navigation is ___________.

What do the couple learn from their experience?

How did people get to know the couple's problem?

It was a winter morning, just a couple of weeks before Christmas 2005. While most people were warming up their cars, Trevor, my husband, had to get up early to ride his bike four kilometers away from home to work. On arrival, he parked his bike outside the back door as he usually does. After putting in 10 hours of work, he returned to find his bike gone.

 The bike, a black Kona 18 speed, was our only transport. Trevor used it to get to work, putting in 60-hour weeks to support his young family. And the bike was also used to get groceries（食品杂货），saving us from having to walk long distances from where we live.

 I was so sad that someone would steal our bike that I wrote to the newspaper and told them our story. Shortly after that, several people in our city offered to help. One wonderful stranger even bought a bike, then called my husband to pick it up. Once again my husband had a way to get to and from his job. It really is an honor that a complete stranger(陌生人) would go out of their way for someone they have never met before.

 People say that a smile can be passed from one person to another, but acts of kindness from strangers are even more so. This experience has had a spreading effect in our lives because it made our confidence in humanity（人性）stronger as a whole. And it has also influenced us to be more mindful(在意的) of ways we can share with others. No matter how big or how small, an act of kindness shows that someone cares. And the results can be continuing forever.

Why was the bike so important to the couple?

We can learn from the text that ________.

According to the passage, the right order of the following is ________. a、 The willow tree gives out a smell. b、 The willow trees make a chemical in their leaves. c、 Insects fly away because of the chemical. d、 Insects begin nibbling a willow tree