One of the following graphs represents the titration of a strong base with a strong acid. Which titration curve is it?

Titration curve showing a strong base being titrated with a strong acid, steep pH change at 30 mL.

Titration curve with a gradual pH decrease, indicating a strong acid being added to a strong base.

Titration curve showing a strong acid being added to a strong base, sharp drop in pH at 40 mL.

Titration curve with a gradual pH increase, indicating a strong base being titrated with a strong acid.