Are the integers z and f to the right of 0 on the number line?
1) product of z and f is positive
2) sum of z and f is positive

I chose e.

From 1. for product to be positive, either z and f are both positive or both negative. Not Suffcient

From 2. for some to be positive, either z and f are both positive or both negative. Not sufficient.

Combing 1 and 2 I think it is still insufficient but the correct answer is C. Can someone please explain?