A. The process of callus formation from in vitro tissues and organs is called dedifferentiation, in which auxin and cytokinin play an important role. A is correct; B, the redifferentiation process occurs in step c, step d is the process of forming artificial seeds through artificial wrapping, and b is wrong; The process of C and B is dedifferentiation. In the process of dedifferentiation, cells undergo severe cell division, and DNA replication will occur during cell division. In this process, mutants with strong resistance can be screened by mutation treatment, and C is correct; D. Artificial seeds can solve the problems of poor reproductive ability, difficult seed setting or low germination rate of some crop varieties, and D is correct. Therefore, it was chosen as B.