Of all the outdoor activities, I like climbing mountains best.  Climbing mountains is a healthy and

  relaxing activity.  Why do I like this activity?  First of all, climbing mountains is a very good exercise. It

 can make people stronger. It's also good for people's heart.  Secondly, climbing mountains is easy and

 cheap.  What you need is a pair of sports shoes and a bottle of water. Thirdly, climbing mountains is a

 good way to get away from daily work or study. One can work or study better after he/ she comes

 back.   Climbing mountains is quite good for people. Would you like to have a try?

（答案不唯一）