A Child Learns the Word Feet, but Several Months Later

Multiple Choice

A child learns the word feet, but several months later stops saying "feet" and instead uses "foots." What seems to be the primary cause (or best explanation) of this change?

A) The child learns foots is easier to pronounce.
B) The child hears other people using the word foots.
C) The child is trying to apply grammatical rules it is learning.
D) The child is reinforced for saying "foots" by parents and siblings who are amused at the error.