When using commas to separate items in a list, place a comma before the conjunction that precedes the last separate item in the list, unless that last item is a compound term. Many people are taught not to place a comma before a conjunction preceding the last item in a list (such as, "red, white and blue"). However, while popular, this approach runs the risk of creating ambiguity in a number of situations. Consider the following. (来源：http://www.EnglishCN.com)

　　Incorrect: The car was available in red, white, black and tan, and special-order colors.

　　上例中，如果车子有四种标准颜色可供选择，则逗号的用法不正确，因为这种用法使人以为车子还有一种复合颜色（black and tan）可供选择。但如果车子只有三种颜色可选，其中一种是复合颜色（black and tan），那么上述用法就是正确的。

　　If the car is available in four standard colors, then the above usage is incorrect, because it implies that black and tan is one, two-tone color option. However, if there are only three color options, one of which is black and tan, then the above usage is correct.

　　Correct: The car was available in red, white, black, and tan, and special-order colors.

　　上例中，放在连词and前的逗号使得读者很清楚，车子共有四种标准颜色的款式，避免了由于在连词and前不加逗号所产生的歧义。

　　The use of the comma before the first conjunction in this sentence makes it clear that there are four standard color options, avoiding the ambiguity created in the first example by the absence of a comma before "and tan."

　　7. 如果有两个形容词一起修饰一个名词时，使用逗号分隔这两个形容词。如果这两个形容词中的第一个形容词是用来修饰第二个形容词的，而不是修饰后面的名词，就不要用逗号分隔这两个形容词。

　　Use a comma to separate two adjectives that modify the same noun, but do not use a comma if the first of two adjectives modifies the second adjective, but not the noun. In considering this choice, ask yourself whether the two adjectives can be reversed. If they can, as in the first example below, separate them with a comma. If they can not, as in the second example below, do not use a comma.

　　Incorrect: The only approach to the city was by a long old highway.

　　Correct: The only approach to the city was by a long, old highway.

　　Incorrect: The suspect drove a light, blue truck.

　　Correct: The suspect drove a light blue truck.

　　In the second example, use of a comma would be incorrect, since "light" modifies "blue," and is therefore not part of a series of commas that modify the word "truck." However, on the off chance that the writer intended to write that the truck was light in weight as well as blue in color, then the first use would be correct. Thus, you can change the meaning of a sentence —— sometimes inadvertently —— by your use of commas.

　　8. 不要用逗号来替代引导词that。

　　Do not use a comma to replace the word "that."

　　Incorrect: The court decided, there is no constitutional right to a second appeal, except by means of a habeas petition.

　　Correct: The court decided that there is no constitutional right to a second appeal, except by means of a habeas petition.

　　Also Correct:

　　The court decided there is no constitutional right to a second appeal, except by means of a habeas petition.

　　In the second correct example, removing the word "that" from the sentence is acceptable because its absence does not confuse the reader. However, leave "that" in a sentence if removing it would create some doubt in the reader's mind concerning what the writer meant to convey.

　　9.不要用逗号分隔一个句子的并列谓语，除非不加逗号会令人费解或是并列谓语的第二部分需要强调。

　　As a general rule, do not use a comma to separate the parts of a double predicate, unless the sentence would be confusing without it, or the second part of the double predicate requires special emphasis. A double predicate exists where the sentence has one subject and two verbs related to that subject. (Please read rule 10 of this section as well.)

　　Incorrect: The customer finished his meal, and paid the check.

　　Correct: The customer finished his meal and paid the check.

　　使用逗号分隔并列谓语来强调的例子：

　　Correct Use of Comma to Create Emphasis:

　　The defendant had been employed as a cashier for twenty years, and never once was accused of stealing money from the register.

　　In the preceding example, the writer creates a greater emphasis on the defendant's innocence by setting off the second part of the double predicate with a comma. Without the comma, the second thought seems like an afterthought.

　　使用逗号分隔句子避免歧义的例子：

　　Correct Use of Comma to Avoid Confusion:

　　The judge ruled that suppression of the evidence was required because it had been obtained illegally, and ordered the defendant released from prison.

　　In this example, the writer avoids confusion by using a comma to introduce the second in the series of compound verbs; without the comma, one might not be sure whether the verb "ordered" related to the subject "it" or the subject "the judge." By contrast, in the sentence above about the restaurant customer, the comma is not needed, because it is a simple sentence.