Bunuel wrote:

Is a product of three integers xyz a prime?

(1) x = -y

(2) z = 1

when can be x*y*z be a prime number..

when any TWO of them give us a product of 1 or -1 that is xy or xz or yz is 1 or -1 and the THIRD is a prime number..

(1) x = -y

when x=1, y = -1, so if z is -3...... 1*-1*-3 = 3 Yes

but if x =2 , y =-2, z any other value , ans is NO

insuff

(2) z = 1

nothing about x and y...

insuff

combined..

z=1..

if x = 1 and y = -1 product = -1...No

any other value of x and y will also give a negative integer..

ans is NO always

Suff

C

_________________

1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372

2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html

3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html

GMAT online Tutor