Concept:Yam can only be improved through breeding if it can reproduce sexually and set seeds, but yam is mainly propagated vegetatively.
Explanation:Breeding involves crossing different varieties to combine desirable traits.
Such crossing requires effective flowers and true seeds.
Yam does not commonly produce functional flowers or true seeds under normal cultivation.
Instead, it is propagated by tubers, which are vegetative parts.
Because yam lacks a practical sexual reproductive system, controlled crosses cannot easily be made.
Its genes do segregate normally, and tuber multiplication is not the main difficulty.
Therefore, the greatest challenge to yam breeding is the absence of a usable sexual reproductive system.
Answer:A. it possesses no sexual reproductive system