The correct answer is option (A):
tea to coffee
The original sentence, "I prefer tea than coffee," is grammatically incorrect. The word "prefer" is used to express a liking for one thing over another. When making this comparison, the word "to" should be used, not "than."
The corrected sentence reads "I prefer tea to coffee," meaning the speaker likes tea more than coffee.
Therefore, the option "tea to coffee" is the correct replacement for the underlined part because it corrects the grammatical error and conveys the intended meaning of preferring tea over coffee.