Certain shipwrecks have a particular fascination for those people which have a belief in finding the treasure in them .

Option (c) depicts the best way of presenting the underlined part as it is grammatically correct and concise. Option (a) is incorrect as the relative pronoun which is used for a thing and not for people. Option (b) is incorrect as it is not clear that they refers to people or shipwrecks. Also, the emphasis is on the finding of treasure in shipwrecks and not simply on the finding of treasure. Option (d) is incorrect as with the word believe, the use of that is more appropriate than the word about in the given context. Hence, option (c) is the correct option.