It is high time we (change) our food habit. Here the correct form of verb is—

The correct answer is (c) changed. Grammar Rule — 'It is high time': After the expression 'It is high time' (or 'It is time'), the verb in the subordinate clause must be in the Past Simple (V2) form, even though the meaning refers to the present or future. Formula: It is high time + Subject + V2 (Past Simple) Example: — It is high time we changed our food habit. ✓ — It is high time he went to bed. ✓ — It is high time they stopped arguing. ✓ ✗ 'change' — Present Simple; not used after 'It is high time'. ✗ 'will change' — Future tense; incorrect in this structure. ✗ 'should change' — Modal verb; not the standard form here. Source: Advanced English Grammar – Martin Hewings (Cambridge); Raymond Murphy.