The correct answer is C. Excessive.
Exorbitant means unreasonably high in price or amount. It can also mean excessive or extravagant in amount, degree, or extent.
Odd means strange or unusual. It can also mean not quite right or normal.
Ridiculous means deserving or causing laughter; absurd. It can also mean extremely foolish or silly.
Threatening means indicating an intention to harm or injure someone or something. It can also mean causing fear or anxiety.
Excessive is the best synonym for exorbitant because it most closely matches the meaning of the word. Odd, ridiculous, and threatening are all words that can be used to describe something that is exorbitant, but they do not capture the full meaning of the word.