X & Y wrote:
Nice trap question. Got C first, but by looking closer you can see that C has a "split infinitive". (WRONG)
Betting on -A-
Nice catch X&Y. Adverb forms are especially notorious because they can pretty much appear anywhere...continue to sharply rise or continue to rise sharply both would appear OK to an unsuspecting campaigner.
I chose A however instantaneously because all the others seemed incorrect.