The correct answer is A.
The key word in the question is "immediate." The dilution of the broth would result in a decrease in optical density, as the same number of microorganisms would be in more broth. So (A) is correct.
(B) might have been tempting, as an increase in nutrients could eventually cause an increase in the growth of microorganisms. However, the
immediate effect would be a decrease in optical density followed later by an increase in the growth of microorganisms.
Choice (C) is incorrect because there is no data to support any conclusion indicating by what factor growth might increase due to an increase in media.
Choice (D) is not correct because, in general, an increase in food supply promotes increases in the population of any living thing, not the reverse.
