This is false: it has a very negative connotation.
It refers to a smile that is mocking or contemptuous (or a remark that is mocking or contemptuos) - so it's not a genuine smile, but an ironic and sarcastic smile. It has a negative and not a neutral connotation.
Hi, I'd sat that the correct answer is B. A cannot be correct, because the simple subject would be "dinosaurs", whereas the complete subject is "large and small dinosaurs", they don't match. C is a similar case - simple subject is "detectives", whereas the complete subject would be "detectives Homer Fry and Janine Small:. In D - simple subject is "crocodiles", whereas the complete subject is "crocodiles, quiet as logs". That leaves us with only one solution - "Cory" is both a simple and a complete subject.
