Taking the two sets of four a bit further though, we can see that if the panel includes F, H, V, and Z in the first year, the panel must include I, F/G, Y, and Z in the second year. If the panel includes I, F/G, Y, and Z in the first year, it may either include I, G/F, Y, and Z or F, H, V, and Z in...

The thing that I find confusing about the proper answer choice (West Nile virus was not carried to NA via and infected person) is that it seems to equivocate between "carrying" and "spreading." The virus could very well have been carried to NA as an isolated case or cases.

I avoided answer (A) just because I didn't understand the usage of the word "obtain."

Quite annoying.