Here's how I see it:
1. tells us that (smallest)*(greatest) is positive means that:
a. both are positive and since they are the "ends" of the series, that makes all the numbers positive. In this case, the product will be positive
b. both are negative, making all of the numbers negative. However, in this case we cannot tell if the product is positive, since we don't know if we have an even or an odd "number" of numbers. Take for example: -5, -4, -3. While it's true that (-5)*(-3) is positive, that cannot be said about the product of the three.

2 doesn't help much. All numbers could be positive, or you could have smth like: -5, 3, 4, 5.

Put the two together and you "eliminate" that weak spot in case b from stmt 1: even if all numbers are negative, they "cancel" each other's minuses. So the OA is ok.

gr8 expln.