The correct answer is answer B "Britannica Online".
Britannica online only contains fact-checked information, so it's a good source that you can always trust.
Using a search engine could give you many un-checked facts or information that may be unsuitable for an essay.
Finally, CNN Interactive will offer very quick updates and is specialized on news items. The problem here, is that this is most definitely a biased source as it's part of a huge corporate network.
Hope this helps!
