What are the necessary components for the development of an infectious plant disease?

In order for an infectious plant disease to develop, all four components - a favorable environment, a plant pathogen, a susceptible host, and time - are necessary. Option B is incorrect because it includes a resistant host rather than a susceptible host. Option C is incorrect because it mentions host immunity rather than a susceptible host and suitable soil instead of a favorable environment. Option D is incorrect because it includes host resistance rather than a susceptible host and mentions suitable soil instead of a favorable environment. Therefore, option A is the best answer as it lists all the necessary components for the development of an infectious plant disease.