A, analysis diagram, Penicillium mutated from A to B, C and D under the action of mutagen, and the output of penicillin was different, which reflected the multi-directional mutation, and A was correct;

B. In the natural state, the mutation rate is very low. Mutants can increase mutation frequency, but gene mutation has no directionality, so it can't determine the direction of mutation. B is wrong;

C. The changes from A to B, C and D in the figure reflect the non-orientation of variation, in which D has the highest yield and is the most suitable variation type for people's production requirements, and C is wrong;

D the mutation of Penicillium under the action of mutagen may include chromosomal mutation and gene mutation, but there is no meiosis and gene recombination, and D is wrong.

So choose: a.