阅读下列短文，根据短文内容，回答下列问题。
Save water, save lives
A BOTTLE of water may not seem like much to you, but it can save the day for people who live in drought-hit (遭受旱灾) areas in China.
In the past few months, some places in southwest China experienced a serious drought. In Yunnan, Guangxi, Sichuan, Guizhou and Chongqing, there has been very little rain since last autumn. Crops died, the land cracked, and wells (井) and rivers dried up. More than 20 million people are having difficulty finding safe drinking water.
After learning about the drought, many people around the country helped by giving water, money and other resources.
Last week, China asked every member of the Communist Youth League (团员) and Young Pioneers (少先队员) to give one bottle of water to the drought-hit area. Students in primary schools and middle schools quickly joined the activity.
“A bottle of water isn’t much, but thousands of bottles will be of great use,” said Zhang Zihao, a middle school student at Tongling No 1 Middle School in Anhui.
In Yuhua Primary School in Xi’an, 900 students bought over 100 bottles of water with their pocket money. They also wrote their wishes on the bottles.
The serious drought has also made students realize the importance of saving water.
Students from Nanshan Middle School in Huizhou in Guangdong went on the street to tell people to take part in water-saving activities.
“I heard that some children in drought-hit areas don’t have enough drinking water. They have to drink muddy (泥泞的) water. I feel really sad about that,” said one student. “I decided to take a shower twice a week instead of every day to save water.” he said.
【小题1】Why did a serious drought happen in Southwest China?
【小题2】What does the underlined（划线的）word “cracked” probably mean in Chinese?
【小题3】What did people do after learning about the drought?
【小题4】Is a bottle of water helpful for the people in drought-hit areas?
【小题5】What can you learn from the passage?
，当ab滑至图示位置时，求拉力的瞬时功率P=？