The correct option is(2) Adventitious root

Explanation:

Sweet potato is a modified adventitious root which is meant for storage of food. It does not assume a definite shape and occurs singly. 

Tap roots develop from the radicle of the embryo. They gradually become narrow towards the tip. Stem is usually the above-ground erect ascending part of the plant body. It bears leaves and flowers. Rhizome is modified underground stem, e.g, Zingiber Officinale.