Dante invented the concept of contrapasso, the idea that sinners should be punished in a way that mirrors or resembles the sin. Dante primarily intended to explain biblical justice through his contrapasso, but in order to do so more effectively, expanded upon tradition, and thus inevitably added some of his own invention.
I'm not sure but it can be a force that pulls objects with mass towards it.
The best answer is a) a general frustration: if everything is going wrong then you can't even find solace in other aspects of life, unlike in D. when if the family life is going well, then the person might at least find some relief there.
