Choose the word which is different from the rest.

The answer is E. Valley.

A peak is the top of a mountain. A mountain is a large landform that rises significantly above the surrounding land. A hillock is a small hill. A mound is a raised area of land, typically smaller than a hill. A valley is a low-lying area between hills or mountains.

The word “valley” is different from the rest of the words in the list because it is the only word that does not refer to a landform that is elevated above the surrounding land.