Read the following paragraph. which sentence is the topic sentence?

i first stopped by the store to pick up a few groceries. then, i dropped off my letters at the post office. i had a dentist appointment in the afternoon. finally, i attended my best friend’s birthday party in the evening. my day was long and exhausting.

(1)- i first stopped by the store to pick up a few groceries.
(2)-then, i dropped off my letters at the post office.
(3)- i had a dentist appointment in the afternoon.
(4)- finally, i attended my best friend's birthday party in the evening.
(5)- my day was long and exhausting.