Well here's something else I learnt this week: a polymer is just a substance whose molecules are made up of the molecules of other substances.
It's obvious when you put it that way; but I don't remember ever thinking of it quite like that before. And for me at least, that made this a surprisingly difficult question to answer (surprisingly difficult, that is, when you know how simple the answer is).
I suspect that the question setter (like me, you may think) is less than an expert in the subject matter – if only because of the inclusion of "momomer" as an alternative answer.
This is another question that seems to have been lifted straight from Wikipedia, which defines a polymer as "a large molecule, or macromolecule, composed of many repeated subunits" (my italics, again).
Wikipedia gives (the Encyclopedia) Britannica as a reference for its definition. On Britannica we read that a polymer is "any of a class of natural or synthetic substances composed of very large molecules, called macromolecules, that are multiples of simpler chemical units called monomers."
In other words, monomers are the "many repeated subunits" that a polymer is made up of. And that's not what the question is asking.
The question might have been more gettable if it had borrowed more wording from Britannica and less from Wikipedia: "What name is given to a natural or synthetic substance composed of very large molecules that are multiples of simpler chemical units?"
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