语法：run-on sentenceCoach Espinoza really wants this job with Notre Dame University,she is very excited about returning to the college she graduated from.这句是run-on sentence,答案说要吧中间的逗号改成句号.那么如果我吧逗号去掉加上一个“and”来连接两句是否可行呢?

书里写的只是一种答案。
你的想法是好的，遗憾的是答案是错的——因为and的作用只是列举，而语境中更需要一个侧重于说明原因的并列连词。
1）Change the comma to another punctuation mark
把错句中逗号改成其他标点符号:
Coach Espinoza really wants this job with Notre Dame University; she is very excited about returning to the college she graduated from.（分号）
2）Write the two clauses as two separate sentences
把错句分写为两个句子:
Coach Espinoza really wants this job with Notre Dame University. She is very excited about returning to the college she graduated from.（此种方法破坏句意关联）
3）Insert a coordinating conjunction following the comma:
Coach Espinoza really wants this job with Notre Dame University, for she is very excited about returning to the college she graduated from.（如前所述）
4）Make one clause dependent on the other
将其中一个分句改为另一个句子的从句:
Coach Espinoza really wants this job with Notre Dame University, because/as(从属连词) she is very excited about returning to the college she graduated from.（原因状语从句）
5）Use a semicolon or dash and a conjunctive adverb
用分号或破折号加连接副词:
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前后句子都有主谓宾,他们都是完整独立的句子,所以不能用逗号或者and隔开.你可以在中间加句号,如果前后句意互相补充的话,也可以用分号.不能用去掉逗号加and,如果你不想用句号或者分号把它们变成两个句子的话,唯一的选...