The correct answer is option 4 - Vegetative propagation. This means that the eyes of a potato are useful for the process of reproducing and growing a new potato plant. The eyes are small indentations on the surface of the potato, and each of them contains a bud. These buds have the ability to develop into new potato plants when they are placed in a suitable growing environment. This process is known as vegetative propagation or asexual reproduction.

Option 1, Nutrition, is incorrect because the eyes of a potato do not play a role in the nutrition of the plant. Option 2, Respiration, is also incorrect because the eyes do not perform the function of respiration. Option 3, Reproduction, is partially correct, but the term "reproduction" is more commonly associated with sexual reproduction rather than vegetative propagation.