Following the idea of Exercise 26, is it possible for an integral domain to contain two subrings isomorphic to Z_p and Z_q for p ≠ q and p and q both prime? Give reasons or an illustration.

Data from Exercise 26

Continuing Exercise 25, is it possible that a ring with unity may simultaneously contain two subrings isomorphic to the fields Z_p and Z_q for two different primes p and q? Give an example or prove it is impossible.