Here's why:

* Tubers are underground stems that are specialized for storing food (primarily starch). Examples include potatoes and yams.

Let's look at why the other options aren't correct:

* Bulbs are underground buds with fleshy leaves that store food. Examples include onions and tulips.

* Corms are short, thick underground stems that store food. They have a solid structure unlike bulbs, which are layered. Examples include gladiolus and crocus.

* Rhizomes are horizontal underground stems that can produce roots and shoots. They can store some food, but their primary function is vegetative reproduction. Examples include ginger and bamboo.

In summary: While bulbs, corms, and rhizomes are all modified stems, only tubers are specifically adapted for energy storage.