Option 1 -> impervious means unable to be affected by something or impenetrable, not related to decision-making speed.
Option 2 -> impetuous means acting quickly without thought or care; impulsive, which perfectly describes someone who doesn't take much time to decide.
Option 3 -> inarticulate means unable to express oneself clearly, unrelated to how quickly one makes decisions.
Option 4 -> inerrant means incapable of being wrong or infallible, which doesn't describe the speed of decision-making.
Hence, Option 2: impetuous -> The sentence describes Sara's tendency to make quick decisions, which is the defining characteristic of being impetuous (acting hastily or impulsively without careful thought) -> correct