Adaptive immunity can be acquired during either 'naturally' (by infection) or 'artificially' (through deliberate actions such as vaccination). Adaptive immunity can also be classified as 'active' or 'passive'
I think the answer to that question would have to be a because its the most reasonable
A poisonous snake of North America is the Rattlesnake... I'm not sure if it's one of only 2, but it is one.