The correct answer is: A. Although
The word “although” is used to introduce a clause that expresses a contrast or concession. In this case, the clause “although he is hardworking” expresses a contrast with the main clause “he is thoroughly honest.” This means that the speaker is saying that the person is both hardworking and honest, even though these two qualities are not always found together.
The other options are not as appropriate in this context. The word “over and above” means “in addition to.” In this case, it would not make sense to say that the person is hardworking “in addition to” being honest, because these two qualities are not mutually exclusive. The word “betimes” means “early” or “promptly.” In this case, it would not make sense to say that the person is hardworking “early” or “promptly,” because these two qualities are not related. The word “along with” means “together with.” In this case, it would not make sense to say that the person is hardworking “together with” being honest, because these two qualities are not necessarily found together.