Choice A reverses the subject and predicate. Choice B is correct but is less effective than choice E because it sets up the two items of information as equal – that stalking is probably as old as human society and its definition. Choice E uses probably as old as human society as an introduction to the focus of the sentence – the definition of stalking. Choice E is also more direct and does not need to repeat the verb is. Choice C uses the phrase the definition of stalking is rather than the more direct stalking is defined as. Choice D puts the definition before the word being defined, which is less effective, making readers wait until they have finished the definition to find out what is being defined.