1. Which of the following sets are rings with respect to the usual operations of addition and multiplication? If the set is a ring, is it also a field? 7 Z 7Z Z 18 Z18 Q ( √ 2 ) = { a + b √ 2 : a , b ∈ Q } Q(2)={a+b2:a, b∈Q} Q ( √ 2 , √ 3 ) = { a + b √ 2 + c √ 3 + d √ 6 : a , b , c , d ∈ Q }