The correct option is
D Interspecific hybridisation
An interspecific hybrid is the product of mating between parents of two different species.
A mule is the offspring of a male donkey and a female horse (mare). Mules are more patient, sure-footed, hardy and long-lived than horses, and they are considered less obstinate, faster, and more intelligent than donkeys.So, the correct answer is 'Interspecific hybridisation'