The correct answer is mountains. Erosion create mountains. It is an act of in which earth is worn away by water, ice and wind. It is the process of weathering, breaks down and dissolution of rocks that create such things. It also create hills and valleys.
The answer is, option a "it can happen in the process of retrieving old memories and combining them with new memories".
Memories aren't correct records of occasions. Rather, these memories are remade in a wide range of routes after occasions happen, which implies they can be misshaped by a few elements. These elements incorporate constructions, source amnesia, the falsehood impact, the insight into the past inclination, the carelessness impact, and confabulation.