Explanation:

- Option 1: tea than coffee

This segment is incorrect. The correct phrasing should be "tea to coffee" or "tea over coffee." When using "prefer," the word "to" is the appropriate preposition.

- Option 2: in the afternoon

There's no grammatical error here. It correctly describes when the action occurs.

- Option 3: after lunch

This segment is correct. It provides additional context and does not contain any errors.

- Option 4: My sister prefers

This is grammatically correct and forms the subject and verb part of the sentence.

Option 1 is the correct answer. Your statement about the error in Option 1 is appropriate.