Children _____ have better memories than adults, especially in learning foreign languages.
A. on average
B. on the average
C. on an average
D. each of
This is a multiple-choice question. I chose A at my first thought, which is right according to the given standard answer. But when I looked up in the dictionary, I found that A, B and C basically have the same meaning. I’m quite confused. Would you please help me in this?