Thanks Tani.
Thanks David.

Sorry to bump this up after so long, but doesn't A suggest that the test subjects themselves suffered from less serious colds-a fact that might have potentially skewed the findings of the study?

No. Choice A gives another effect of the potential cause - zinc applied nasally. This is only another effect and can never be an alternate cause.

For example, if I say that when I eat peanut butter sandwiches I get sick and I think the cause is peanut butter, it is never going to weaken this to say that I get sick and break out in a rash. That is another effect. I can weaken the cause - peanuts - by saying I might be allergic to bread instead. That is an alternate cause.

So do not look to weaken a cause and effect with another effect.

Thanks David, I'm still a little confused though, do you mean the symptoms were found to be milder after applying the nasal spray or were the symptoms of the cold bad recorded before applying the same?