First sentence
1-> there was growth in dairy farms in city
2->mutationin the gene of people in that locality,
3->they can digest milk products.
so if (1&2)->3.
option A. is completely wrong as everyone can digest milk products(FALSE)
option B. Everyone can digest milk but we got no reason that how can we digest( FALSE)
option C. Mutation in the genes is needed to digest milk products, As from paragraph we know that it was a coincidence between sentence 1 and sentence 2, so Happening of sentence 2 is very much the cause of the sentence 3.(TRUE).
option D. as we know sentence 1 and sentence are coincidence so there is no connection that increase in dairy products can cause mutation in people(FALSE)