Identify which one of the following sentences contains an unnecessary comma. Please correct the error and explain why the correction is necessary.

A. I must have been completely absorbed in my work, because I totally forgot about the meeting.
B. Because I became completely absorbed in my work, I totally forgot about the meeting.

A. has an unnecessary comma.

This site explains this incorrect comma usage.
http://owl.english.purdue.edu/owl/resource/607/02/

Thank you Ms. Sue! =)

You're welcome, Yonaa.

The sentence that contains an unnecessary comma is sentence A: "I must have been completely absorbed in my work, because I totally forgot about the meeting."

The correct version of this sentence would be: "I must have been completely absorbed in my work because I totally forgot about the meeting."

The unnecessary comma in the original sentence is placed before the word "because". This is not needed because there is no independent clause following the word "because". In this case, the word "because" is introducing a dependent clause ("because I totally forgot about the meeting") that explains why the person must have been completely absorbed in their work. When a dependent clause comes before an independent clause, typically no comma is needed. However, if the sentence were to be reversed, with the independent clause coming before the dependent clause, a comma would be necessary.

Therefore, the correction is necessary to conform to proper punctuation rules and clarity, by removing the unnecessary comma before "because".