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.