如：Asking around, I find many people willing to pay slightly higher prices for things that are environmentally friendly. =When I ask around, I find many people willing to pay slightly higher prices for things that are environmentally friendly.
Having observed the problem for many years, he announced that we are now facing the biggest environmental problem of our time. = After he observed the problem for many years, he announced that we are now facing the biggest environmental problem of our time.
2）原因
如：We are making bigger holes in the nets, hoping to avoid catching fish that are not fully grown. = We are making bigger holes in the nets, because we hope to avoid catching fish that are not fully grown.
3）结果
如：The factory keeps releasing smoke, making the air dirty. = The factory keeps releasing smoke. As a result, the air is made dirty.
4)条件
如：Preparing fully, we can achieve great things. = If we prepare fully, we can achieve great things.
2．连词+v-ing 也可以来表示时间。常用的连词有：when whenever while once until 如：We have to take environmental protection into consideration when developing the economy.
3．v-ing 从句的逻辑主语通常和主句的主语一致。
如：He traveled on the plane like this, keeping the tortoise in a blanket. = When he traveled on the plane like this, he kept the tortoise hidden in a blanket.
4．否定形式是： not+v-ing
如：He sat there, not knowing what to say.
第三单元
一 V-ed形式
v-ed在句中可以充当形容词和副词的用法。
1．v-ed可以被用作：
1）定语
v-ed放在名词的前面，像形容词一样修饰名词。V-ed可以改成定语从句。
如：If I had the chance, I would have a cloned baby.= if I had the chance, I would have a baby who is cloned.
大部分名词前的v-ed表达被动的含义。但有些v-ed 表达过去的含义，如，escaped retired fallen。比较下面的短语：
表被动：the highly praised scientist ( The scientist has been highly praised.)
表过去：the retired scientist (The scientist has retired.)
有时候可以把副词放在v-ed之前。
如：well-trained teachers
v-ed 可以和副词或名词连用构成复合词。
如：underdeveloped region handmade furniture
v-ed可以像定语从句一样放在名词后修饰名词。
如：I think the scientific advances mentioned in your article are interesting.= I think the
