Answer: I would contend that the solution that does NOT correctly fix the following run-on sentence is the A) They were expensive combs, her heart had simply craved and yearned over them.
Explanation: Just to elaborate a little on the answer, it can be added that "They were expensive combs her heart had simply craved and yearned over them" is an example of a fused sentence — two independent clauses run together without the proper separation (a coordinating conjunction or the appropriate punctuation mark). The solution presented in option A is actually another example of a run-on sentence, specifically a comma splice, since the two independent clauses have been joined just by a comma. However, the solutions B and C are correct, since a run-on sentence can be fixed by using a comma FOLLOWED BY a coordinating conjunction (B) or by separating the two clauses into sentences by means of a period (C).