Choose the grammatically correct sentence:

The correct answer is Option (1) → Grandmother says that growing our own vegetables is cheaper than buying them at the mandi.

Two actions compared with “than”:

• When two actions are compared with “than” or “as”, both must be in the same form.
• Here the first action is “growing”, an -ing form. So the second must also be an -ing form: than buying them.

Why the Other Options are Incorrect?

Option 2: Grandmother says that growing our own vegetables is cheaper than to buy them at the mandi. — Incorrect. The option says “growing ... than to buy”. An -ing form is compared with a to-form, so the two sides do not match.

Option 3: Grandmother says that to grow our own vegetables is cheaper than buying them at the mandi. — Incorrect. The option says “to grow ... than buying”. A to-form is compared with an -ing form, so the two sides do not match.

Option 4: Grandmother says that growing our own vegetables is cheaper than buy them at the mandi. — Incorrect. The option says “than buy them”. The plain verb “buy” does not match the -ing form “growing”.