**Explanation:**

**Introduction:**
Angiosperms and gymnosperms are two major groups of seed-bearing plants. They have several differences in their reproductive structures and adaptations. One of the key differences between these two groups is the presence or absence of fruits.

**Angiosperms:**
Angiosperms are flowering plants that produce seeds enclosed within a protective structure called a fruit. Fruits develop from the ovary of the flower after fertilization. They are diverse in form and function, ranging from fleshy fruits like apples and oranges to dry fruits like nuts and grains. The presence of fruits is a characteristic feature of angiosperms and distinguishes them from gymnosperms.

**Gymnosperms:**
Gymnosperms, on the other hand, do not produce fruits. Instead, they have naked seeds that are not enclosed within a fruit. Gymnosperms include plants like conifers, cycads, ginkgoes, and gnetophytes. They produce cones or strobili that contain the naked seeds. The lack of fruits is a distinguishing feature of gymnosperms.

**Difference between Angiosperms and Gymnosperms:**
The main difference between angiosperms and gymnosperms is the presence or absence of fruits. Angiosperms have seeds enclosed in fruits, while gymnosperms have naked seeds.

- Angiosperms: Seeds enclosed in fruits
- Gymnosperms: Seeds not enclosed in fruits

**Conclusion:**
The option C, "Seeds enclosed in fruits," is the correct answer because it is the characteristic feature that most differentiates angiosperms from gymnosperms. While angiosperms have evolved the ability to produce fruits to protect and disperse their seeds, gymnosperms have not developed this adaptation. Thus, the presence or absence of fruits is a key distinguishing feature between these two groups of plants.