Answer:
The answer is c "It is a crime even if the extortion message is sent either unwillingly or without the knowledge of the sender."
Explanation:
Extortion, in most countries, means obtaining something by coercion or threat. Thus, if a message is sent through a mobile phone of someone with the person's knowledge or not, then an act of extortion may have been established. The onus is on the owner of the phone to prove innocence of sending such message in the first place while he may be charged with extortion as the case is established.