I did mine on the Mystery Religions. A Catholic on my committee would not let me include catholiciism ... but it belong in the category.
Here is the missing “s”.
“I did mine on the Mystery Religions. A Catholic on my committee would not let me include catholiciism ... but it belong in the category.”
No, your committee member was right. They are there to keep the student from making a mistake and looking foolish. You could still use one even now.