What Does the Phrase "A Not B Error" Mean

Multiple Choice

What does the phrase "A not B error" mean?

A) Children will not search for hidden objects unless given an incentive.
B) Children will randomly search for hidden objects, but will quickly become frustrated and give up.
C) A child may reach for a hidden object where it has always been, yet still reach there even when they see the toy hidden somewhere else.
D) A child will search for a hidden toy but will quickly become distracted by other, more interesting objects.