Identify the incorrectly punctuated sentence.

All of the sentences are correctly punctuated.

On the morning of June 28, 1948, I walked down to the post office in our little Vermont town to pick up the mail. I was quite casual about it, as I recall - I opened the box, took out a couple of bills and a letter or two, talked to the postmaster for a few minutes, and left, never supposing that is was the last time for months that I would pick up the mail without an active feeling of panic.

A. in our little Vermont town
B. active feeling of panic
C. talked to the postmaster for a few minutes
D. I opened the box

B. active feeling of panic (it should be "an active feeling of panic")

The incorrectly punctuated sentence is:

B. I promised to be on time for the art show so that I could help sign up the participants.

The correct punctuation should be:
I promised to be on time for the art show so that I could help sign up the participants.

To identify the incorrectly punctuated sentence, we need to review the punctuation in each sentence option. Looking at each sentence:

A. "I went to the library and checked out two books, a movie, and an audio recording." - This sentence is correctly punctuated. It uses commas to separate the items in a list.

B. "I promised to be on time for the art show so that I could help sign up the participants." - This sentence is correctly punctuated. It uses a comma to separate the two clauses in the sentence.

C. "I want to learn more about Ireland, but my classmates prefer to study Scotland." - This sentence is correctly punctuated. It uses a comma to separate the two independent clauses.

D. "My homework includes reading a story, writing a paragraph and finishing some math problems." - This sentence is incorrectly punctuated. It is missing commas between "writing a paragraph" and "finishing some math problems." To correct it, we need to add commas after "paragraph" and "problems." The revised sentence would be: "My homework includes reading a story, writing a paragraph, and finishing some math problems."

Therefore, the incorrect punctuated sentence is D.