The correct option is B The introduction of disease resistant varieties
Selection of disease resistant variety come after its introduction. The introduction of disease resistant varieties is the primary and most important step to control the disease. These varieties protect the plants from diseases causing organism by producing preformed toxins and by infecting immune cells of pathogens. The breeding of permanent resistant varieties is not a method of control diseases. Biological control is done by the use of biopesticide which takes a time to kill pathogen and it is not the permanent solution. Thus, the correct answer is option B.