（1）引导词as
结构1：as +形容词/副词+ as
a. The work is not as difficult as you think.
b. Eyes are as eloquent as lips (are).
结构2：as +形容词+ a (n\2) +可数名词单数+ as
c. Americans tend to think from small to large. Let us take as simple an example as the addressing of envelopes.
美国人思维喜欢由小到大。我们以写信封地址这样一件小事为例。
d. I didn’t finish as large a part of the work as he did.
注意：在否定句中第一个as可用so代替。
（2）引导词than
1）两个同类事物之间才能比较，如he和I。两个非同类事物之间是无法作比较的。
a. He is taller than I (am).
b. The weather of the South is wetter than the North.*
b句是典型的错误句子，因为the weather of the South和the North是两个截然不同的事物，无法进行比较。只能是“南方的天气”和“北方的天气”两个同类事物才能比较。故原句应该改为：
The weather of the South is wetter than that of the North. （为 避免重复，用that代替the weather）
c. Young readers, more often than not（A）, find the novels of（B） Dickens far more（C） exciting than Thackeray（D）.
正确答案：D，应改为Thackeray’s。这里比较的对象是两个作家的小说。Thackeray’s等于Thackeray’s novels。
2）在有than的比较句子里，主句中必须有比较级形式出现。
a. He has made great contributions to the company than anyone else.*
（此句中应将great改为greater）
b. On the whole（A）, ambitious students are much likely（B） to succeed in their studies than those（C） with little（D） ambition (are).
正确答案：B，应改为more likely。
（3）“the more…（主句）， the more…（主句）”句型表示比较
a. The more she practiced, the worse she sang.
她练习得越多，唱得越糟糕。
b. The nearer it is drawn to the surface of the earth, the more a body weighs.
一个物体离地球表面越近，重量就越大。
c. The higher you go, the less dense air becomes.
你登得越高，空气就会变得越稀薄。
d. The more we help others, the more we receive in return. We advance ourselves as we help others.
帮助别人越多，我们获得的回报也越多。帮助了他人就是在提升自己。
e. Friends are lights in winter: the older the friend, the brighter the light.
朋友犹如冬日里的暖阳，愈久弥珍。
f.The more you leave things to chance, the less chance there is for you.
你越是听天由命，留给自己的机会就越少。