Concept:Biotechnology involves the use of living cells and tissues to propagate plants or organisms.Explanation:Propagation in biotechnology is mainly done through cell and tissue culture techniques.In this method, small pieces of plant tissue or cells are grown in a sterile nutrient medium to produce new plants.This is known as micropropagation, and it is a key biotechnological tool for rapid multiplication.The other options—grafting, aerial layering, and binary fission—are not the main biotechnological propagation methods.Answer:D. cell culture.