Granted, it is not a very smart question given the multiple meanings of the words given. But then it is not a question of semantics.
Being part of a test given to job applicants, it is not for you to question the question, ask for context etc. or prove that you are smarter than the one who set the question.
The objective is give the best answer, with the given words.
You are asked to choose a pair of opposites out of three words - extension, condensation and subtraction.
Extension and subtraction have a common denominator in that they about a change of size/quantity of something, as in addition and subtraction.
Why would one consider the idea of extension of a rubber band which springs back to its original size? Or condensing a paragraph of words to make it shorter? Both of which would not lead you to any answer.