由OG 12 SC 87引发的一个小问题，求指导！

japlir

In an effort to reduce their inventories, Italian vintners
have cut prices; their wines have been priced to sell,
and they are.

(A)    have been priced to sell, and they are
(B)    are priced to sell, and they have
(C)    are priced to sell, and they do
(D)    are being priced to sell, and have
(E)    had been priced to sell, and they have

OG对D的解释中，说omitting the subject they requires that the comma be omitted as well.
对于and前何时用逗号何时不用逗号很疑惑！
一般三个并列的时候A,B,and C第三个并列元素前不都是要用逗号和并列词and 么？
彻底困惑了，
求NN帮助区分：什么时候and 前要逗号，什么时候不能要逗号？


另外，附上一个问题:OG解释中的comma splice是什么语法错误？和run-on sentence是一回事么？

aeoluseros

参见这个帖子里的run-on sentence:
http://forum.chasedream.com/GMAT_SC/thread-81945-1-1.html

powers

and后+平行的东西的时候前面不加逗号 --做介词的时候

and后加句子(出现主语)的时候,前面要加逗号 --做连词的时候

powers

d选项, and前面有逗号,后面句子没主语.成分不全

japlir

and 还可以作介词么？
前面不加逗号是连接三个平行的名词、形容词成分么？

如果and 后出现动词，但是由于是相同主语省略了，也不使用逗号么？

japlir

不好意思！打错了，是问comma splice 是不是等同于run-on sentence ？是么?

japlir

不好意思各位NN，我还是没弄明白，可以回答我的问题么？

FactOrFiction

我查了下wiki.

A run-on sentence is a sentence in which two or more independent clauses (i.e., complete sentences) are joined without appropriate punctuation or conjunction. It is generally considered to be a grammatical error though it is occasionally used in literature and may be used as a rhetorical device. An example of a run-on is a comma splice, in which two independent clauses are joined with a comma without an accompanying coordinating conjunction.

所以comma splice是run-on的一种情况.