Select the sentence that is grammatically correct:

The correct answer is Option (1) → You had better book the tickets today, as the Diwali trains fill up very fast.

“Had better” + base form of the verb:

• “Had better” gives strong advice. It is followed by the base form of the verb, without “to”: “had better book”.
• Here “had” does not show the past. The advice is about today.

Why the Other Options are Incorrect?

Option 2: On our school trip, we saw the huge dam built across Mahanadi near Sambalpur. — Incorrect. The name of a river takes “the” before it.
Corrected: On our school trip, we saw the huge dam built across the Mahanadi near Sambalpur.

Option 3: The water level in the lake has raised by two feet since Monday. — Incorrect. The water level goes up by itself, so the verb is “rise”, not “raise”. “Raise” needs an object, as in “raise your hand”.
Corrected: The water level in the lake has risen by two feet since Monday.

Option 4: Although the shop was crowded, but the owner found time to talk to us. — Incorrect. “Although” already joins the two parts, so “but” is not needed.
Corrected: Although the shop was crowded, the owner found time to talk to us.