Final answer:
The original sentence is grammatically correct, so option C (No improvement or correction is required) is the right answer. Other options are merely alternative phrasings and not corrections.
Step-by-step explanation:
The sentence "Relief came to everyone involved in the tragedy when the attorney settled the case out of court." does not contain a grammatical mistake, so option C, No improvement or correction is required, is the correct answer.
Options A, B, D, and E are alternative ways of restructuring the same idea, but none of them are necessary to correct a grammatical error in the original sentence.
It's important to keep the focus on the fact that the relief experienced by those involved was a result of the attorney settling the case, which is clearly conveyed in the original sentence.
So option C.