1. He waved desperately to his companion, who had been water- skiing for the last fifteen minutes.
    他拼命向他的同伴挥手，这个同伴在刚才十五分钟里一直在水上滑水撬。

2. He waved desperately to his companion, who had been water skiing for the last fifteen minutes.
    他绝望地向他的伙伴挥手，他的伙伴在过去的15分钟里一直在滑水。

3. You must have special boots for skiing.
    滑雪必须穿特别的靴子。

4. Let´s go skiing.
    我们滑雪去吧。