Explanation:

- Extortion (Option 1): A induces B to sign the paper by putting B in fear of grievous hurt. This is a classic case of extortion, where the consent is obtained under threat.

- Robbery (Option 2): Robbery involves taking property directly from a person with intent to permanently deprive them of it, using force or threat. In this scenario, the main element is inducing fear, but it does not constitute robbery as nothing is being physically taken from B.

- Cheating (Option 3): Cheating involves deceit to obtain property or induce a person to act to their detriment. Here, the emphasis is on fear rather than deceit, so it does not fit the definition of cheating.

- Dacoity (Option 4): Dacoity involves robbery committed by a group of five or more. As the situation involves only A and B, it doesn't qualify as dacoity.

Extortion is the correct answer.