Fill in the blank with appropriate option.You _ reduce the speed. There is a speed limit.

Explanation

The correct answer is "Must" because it denotes a strong necessity or obligation to reduce speed immediately due to the speed limit, making it mandatory. "Need to" and "Ought to" suggest less urgent obligations or recommendations, lacking the imperative nature of "must." "Will" indicates a future action, which does not fit the context of needing to reduce speed right now.