I think it would be D or B. The tone is mysterious, which seems pretty close.
Answer:
Explain the question on the school page first
Explanation:
Adding -s is the most common. for example: books, cups, pencils, etc. -es might have been the one that confused you, but that isn't a super common ending for plurals--instead, a more common one would be "-ies" which is when you drop the y (berry becomes berries, for example).
