I do not like the wording of the question to be honest. IF there is an even number in the set then no matter what happens the set will always have an infinite number of even numbers and there is no chance for an odd number to sneak in. However the question asks which one of the below MUST be in the set which IMO is not fair!! If we know that the set is a set of odd numbers then I will go for all of the above i.e. I,II and III. But if there was a None in the options I would have chosen that instead. Whts the source of these questions????

Old GMAT paper Tests.

Ian Stewart wrote:You've certainly left out part of the question, since it can't be answered as written. As written, it says:

A set of numbers has a property that for any number t in the set, t+2 is in the set, which of the following must also be in the set?

The word 'also' makes no sense here, since the question hasn't yet mentioned any number which is in the set. The question surely reads something more like "if -1 is in the set, which of the following must also be in the set?" in which case the answer would be D.

Yes Ian, I did the same thing, but the answer is E. I copied the question properly.There is no typo error.