Could you clarify what you mean when you say "alternate answer choice?" On the LSAT the four wrong answers are always wrong, and there is only one right answer. There's never a situation in which there is a 'second-best' answer, as the wrong answers always have at least one flaw that makes them patently incorrect.
Irrelevant answer choices are ones that do not add anything to the argument and the relationship between the premises and the conclusion. In cause and effect questions, this means that irrelevant answer choices simply won't have anything to do with what's being described in the stimulus.
Hope this helps. Let us know if you have any other questions!
