In this context, I think the intended meaning is a), thus the object is "some sentences similars to yours" and 'requiring' would be necessary.Either is acceptable. I, however, wouldn't make a habit of dropping the "have" verb, you'll find some sentences similar to yours require it.
navi tasan said:Thanks a lot Theschnitzel.
Could you give me a sentence that requires it?
Sorry to disagree with you François, but as far as I can see there is nothing wrong with "require it" here: "You'll find (that) some sentences require it." The "that" can be omitted. I am not really sure that "requiring" works well in this context (if we put in the "that", it would definitely be wrong).