Mark each of the following true or false. 

___ a. nZ has zero divisors if n is not prime. 

___ b. Every field is an integral domain. 

___ c. The characteristic of nZ is n.

___ d. As a ring, Z is isomorphic to nZ for all n ≥1. 

___ e. The cancellation law holds in any ring that is isomorphic to an integral domain. 

___ f. Every integral domain of characteristic O is infinite. 

___ g. The direct product of two integral domains is again an integral domain. 

___ h. A divisor of zero in a commutative ring with unity can have no multiplicative inverse. 

___ i. nZ is a subdomain of Z. 

__ j. Z is a subfield of Q.