The correct answer is option 4: stem. Ginger is a modified stem. A stem is an important part of a plant that provides support and connects the root system with the rest of the plant. In the case of ginger, the underground part that we commonly use is actually the rhizome, which is a type of modified stem. The rhizome of ginger grows horizontally underground and has nodes and internodes like a regular stem. It also produces roots from the nodes and shoots from the internodes. The edible part of ginger that we use in cooking is actually the rhizome, which is the modified stem. The stem-like nature of ginger can also be observed as it grows above the ground, where it produces leaves and flowers.