Explanation:

- Cheating: Involves deceiving someone to gain a dishonest advantage. It doesn't involve putting someone in fear of death.

- Robbery: Involves taking property from someone with the intention of permanently depriving them of it, often using violence or threat of violence.

- Mischief: Involves causing wrongful loss or damage to property, but it doesn't include fear of death to obtain a sum.

- Extortion: Obtaining something of value by putting someone in fear of injury or death. This aligns with the action of obtaining money by putting B in fear of death.

Correct Answer: Extortion