B is the answer to this question. This is the process wherein there is contact between two surfaces that should not be connected. Based on the illustration, it shows that M to F shows unconformity. The main reason why this may occur is because of erosion.
There may be some parts of the rocks or the soil that have eroded because of heavy rain or floods. The gaps can be dangerous especially in high places because this makes it more likely for a whole portion to break apart. Another reason why this may happen is when rock deposits fail to form even if they are expected to develop.