Consider a kirby-bauer disk-diffusion assay. if you put penicillin and streptomycin disks adjacent to one another, the zone of inhibition is greater than that obtained by either disk alone. this is an example of
a. rna interference
b. mutual exclusion
c. synergism
d. antagonism

This is an example of synergism.

Explanation:

synergism is the motion of two or more than two trans- acting agents that given at a same time which is greater than the sum of activity had those agents if given separately. They are steroid receptors, which acts as response for saturating concentration of the steroids.  The synergism of the steroid receptors among themselves or with anti-infective factors at saturating concentration of steroid has showed to be very important component for steroid regulated gene transcription.