Choose the most suitable option to replace the highlighted part of the sentence:

It is high time you must follow a proper routine.

The correct option to replace the highlighted part is followed a proper routine.

Explanation and Grammar Rule:

In English grammar, phrases like "It is high time", "It is time", or "It is about time" are used to indicate that something should have been done already, or that an action is past due.

When these phrases are followed by a subject (in this case, "you"), the verb that follows must be in the simple past tense (subjunctive mood) to express an unreal or hypothetical present/future situation.

Structure:
It is high time + Subject + Simple Past Tense (V₂)

Analysis of the sentence:
Given sentence: "It is high time you must follow a proper routine."
Here, "must follow" is incorrect because modal verbs like must should not be used after "It is high time" when a subject is present.

Replacing "must follow a proper routine" with the simple past form "followed a proper routine" makes the sentence grammatically correct:

"It is high time you followed a proper routine."