Statement I:

Tells us the list of numbers are either negative or positive:

Ex: -4, -2, -1 etc.
or 4, 2, 1 etc.

InSuff.

Statement II:

Tells us the list has an even amount of #s

Ex: -1, 1, 2, 4
Ex: -3, -2, -1, 1

Insuff.

Together:

If all the numbers in the list are either positive or negative, and there's an even number of them, then the product of those numbers will always be positive.

Hope that helps.