The answer is B because A is 'your is' so that's wrong because that would make the sentence 'my fear is greater than your is' which is grammatically incorrect. C is 'your' which would make the sentence 'My fear of insects is greater than your' and that's not proper English. And D is 'you are' so the sentences ends up 'My fear of insects is greater than you are'. Though it may sound okay, it's still wrong because of the meaning of the sentence. B is 'My fear of insects is greater than yours' which would be correct for English grammar.
