~~~ the most + 形容词 + 名词 + + 主词 + have ever + seen any pollution. 使用太阳能的优点是它不会制造任何污染。

　　八、The reason why + 句子 ~~~ is that + 句子 (...的原因是...)

　　例句：The reason why we have to grow trees is that they can provide us with fresh air./ The reason why we have to grow trees is that they can supply fresh air for us. 我们必须种树的原因是它们能供应我们新鲜的空气。