The correct option is C to realize the scam
A finite clause contains a verb that shows tense whereas a non-finite
clause contains a verb that does not show tense. The latter is often
seen in subordinate clauses, where the tense is figured out through the
main clause.
Option C is correct as the clause "to realize the scam" does not show any tense, hence it is a non-finite clause.
Option A is incorrect because "took" is a verb in the past tense, hence the clause is finite.
Option B is incorrect because "to realize" is an infinitive phrase and not a clause.
Option D is incorrect because the words do not form a clause, also, the verb in the past tense "took" is included.