What Happens in the Fallacy of the Undistributed Middle

What happens in the fallacy of the undistributed middle?

A) The major and minor terms are not directly linked by the middle term because the major term is undistributed.
B) The major and minor terms are not directly linked by the middle term since either the major or minor term is undistributed.
C) The major and minor terms are not directly linked by the middle term since the minor term is undistributed.
D) The major and minor terms are not directly linked by the middle term, since the middle term is not distributed in at least one premise.