3. cost/ take/ spend/ pay
(1) cost表示"花钱"，花费，付出（只能用于钱、精力、生命等；主语必须是物。）
  The book cost me five yuan.
(2) take的主语是动词不定式, 通常用it做形式主语。
It took me five yuan to buy the book..
(3) spend，在主动语句中主语是人
I spent five yuan on (for) the book.或I spent five yuan (in) buying the book.
(4) pay的主语是人。
I paid five yuan for the book.

4. expensive/ high/ cheap/ low
    这四个词在谈论到价格的高低时，要注意使用。expensive与high涉及到价格"高"，而cheap 与low涉及到价格"低"。
  (1) expensive昂贵的，花钱多的。这个单词若谈到"价格高，货贵"时，其主语不能是价格，必须是货物、物品本身。如：
   This watch is expensive. 这只表很贵。
   These glass-products are not expensive. 这些玻璃制品不是很值钱。
注意：cheap表示"价廉"，"便宜的"，其主语也不能是价格，必须是物品本身。如：
The cheap table was bought from him. 这张便宜的桌子是他卖给我们的。
This cloth doll is very cheap. 这只布娃娃很便宜。
(2)high在表示价格时，含义是"高"，low在表示价格时，含义是"低"，这两个词不能用于物品本身，只
能用在价格上。如：
The price of this watch is very high. 这只表的价格太高了。
The price of this book is not low for me. 这本书的价格对我来说是不低。
下面我们试看几个句子的正误对照：
The price of this computer is expensive.
(宜改为：This computer is expensive. 或The price of this computer is high. )
The price of this pen is not cheap for him to buy.
(宜改为：This pen is not cheap for him to buy. 或 The price of this pen is not low for him. )

5. alone/ lonely
    lonely 与alone的意思比较接近，但在使用时有所区别：
(1)lonely用作形容词，意思是"孤单的；寂寞的"。可指心灵上的寂寞，也可指偏僻的地点。在句中既可作表语，也可作定语。
(2)alone 可作形容词和副词，意思是"单独；独自"，不指心理上寂寞的感觉。
She was taken to a lonely island, lived alone, but she never felt lonely.
她被带到一个荒岛上，自己居住，但她从不感到寂寞。
6. before long/ long before
(1)before long 作“不久以后”讲，切不要按字面译为“长时间以前”或“好久以前”。如：
We hope to finish our experiment before long. 我们希望不久（以后）就把实验做完。
(2)long before 作"很久以前"讲。原意为"……以前很久"，故也可译为"老早"。long before 跟before long
不同，前者在其后面可以接名词或一个从句；当上下文明确时，名词或从句还可以省略。Before long 则没有上述搭配用法。
    They began the test yesterday, but we had made experiment long before.
我们昨天开始做实验，但我们在那以前很久就已经做准备了。