Caustic is to corrosion as frenetic is to (C) activity. Caustic is a word that means to corrode or fade away. Frenetic is a term that means uncontrolled, fast, and lots of energy, which relates to the answer of activity.
Caustic means corrosive.Then frenetic means active in a way that means frantic , with too much activity.We have caustic as an adjective that has a similarity to the noun corrosion the same way we have the adjective frenetic as a synonym or near synonym of the noun activity.
