In order to get two marks, you have to write more then one sentence. If you find that you can't elaborate (e.g. for validity you could elaborate by talking about internal/external validity) then you either contextualize it to the study given above (if it asks you) or give a well known example from a core study you did last year (e.g. for a field experiment, you could use Langer and Rodin who conducted theirs in a care home). Trust me, it isn't a waste of time, you've just gotta see whether it's two mark worthy to get the marks in the bag.