Translation:Christianity is the largest religion in the world.
I think that this statement is repeated too many times in the exercise. I don't want to say 'greatest' for ΄μεγαλύτερη' in this context but presumably it could be translated as 'greatest', couldn't it?
I don't understand what you mean by "this statement is repeated too many times in the exercise". Do you mean that you have been required to translate the same sentence many times? Depending on how many times it might be a usual occurrence or a technical glitch. So, how about how many times was it repeated?
Ιn this case, "μεγαλύτερη" as you can see in the heading above is translated as "largest" "biggest" is also accepted. "Greatest" does not fit since the statement refers to quantitative data. Only if it said "the greatest number of members" could it be used.