1. Now that we have seen these great achievements with our own eyes, we feel more
　　　　proud than ever of our country.
　　2. Professor Liu is strict with us because he wants us to make rapid progress.
　　3. Since we live near the sea, we enjoy a healthy climate.
　　4. Pollution is still a serious problem, not that we don`t have the ability to solve it, but that
　　　　some people have not realized the consequences of the problem.
　　我们还可以借助某些词语用简单句表达原因结构。例如：
　　1. The reason for this change is quite obvious.
　　2. Diligence is the key factor of success.
　　3. Idleness is the root of all evils.
　　4. He was ashamed to have made the mistake.(=He was ashamed that he had made the
　　　　mistake. =He was ashamed because he had made the mistake.)
　　除了上述的例句外，英语中还有很多或易或难的表达原因的结构。我们在进行写作训练的时候，不能满足于一知半解，要讲究书面语言的正确性和准确性。比如，because是最常用的引导原因从句的连词，语气最强，表示直接的原因，若because置于句首，后面的主句不能再用so。用as引导的原因从句语气较弱，所说明的原因是附带的，而since表示的原因暗示着是稍加分析之后才能推断出来的原因。
　　四、 否定结构
　　考生病句
　　1. Some people think we needn`t to worry about fresh water.
　　2. Nowadays many people don`t like to go to the movies, too.
　　正确表达：
　　1. Some people think we needn`t worry (或don`t need to worry) about fresh water.
　　2. Nowadays many people don`t like to go to the movies, either.
评议与分析：
　　例句1选自96年1月四级考生作文，例句2选自92年1月六级考生作文。例句1 的错误在于该考生混淆了need作为情态动词和作为普通动词的用法。need作为情态动词时，主要用于否定句，后面的动词不带to, needn`t worry，作we的谓语。need作为实意动词时，可用于肯定句、否定句和疑问句，don`t need to worry 中的to worry作don`t need的宾语。例句2的错误在于该考生混淆了too和either的区别，这两个词都表示"也"的意思，但是在英语中too, also只能用于肯定句，而either只能用于否定句。