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.

A) I first stopped by the store to pick up a few groceries.

B) Then, I dropped off my letters at the post office.

C) I had a dentist appointment in the afternoon.

D) Finally, I attended my best friend's birthday party in the evening.

E) My day was long and exhausting.