Fill in the blank with appropriate option.You _ drive fast. We have plenty of time.

Explanation

The correct answer is 'Need not' because it indicates that there is no necessity to drive fast due to the availability of ample time. 'Will not' and 'Shall not' suggest future actions, which are not relevant to the present context. 'Must not' indicates prohibition, which does not align with the relaxed implication of the sentence.