Which sentence contains a mechanical error?

the class opened its writers inc books to the chapter titled "writing basic essays."
we were supposed leave friday for our trip to puerto vallarta, mexico, but we had to cancel.
her birth records indicate she was born on november sixteenth, 1961.
callie's piano lesson is at 4: 00 p. m. every monday and wednesday.

in this passage from "animal farm", by george orwell, the statement that best explains how boxer's response supports the author's purpose in writing an allegory is option b) orwell uses boxer's decision to avoid more carnage by working hard to show how the working class was manipulated. boxer and the other animals feel they are responsible for their carnage because napoleon uses propaganda to manipulate the animals of the farm.

explanation: