Topic: Degree of Comparison,

Best Answer Explained in Below-:

The sentence "I prepare my lesson - than you." requires a comparative form to effectively convey that the speaker's lesson preparation is being compared to someone else's. The term "than you" indicates a comparison, necessitating the use of a comparative adverb in the blank.

Among the options provided:

- A) "carefully" is an absolute form and does not express a comparison.
- B) "so carefully" suggests a high degree of carefulness but doesn't facilitate a comparison.
- C) "most carefully" indicates the highest degree but is not appropriate here as it implies a superlative rather than a comparative context.
- D) "more carefully" is the correct choice as it clearly juxtaposes the speaker's preparatory efforts against those of the person being addressed.

Using "more carefully" implies that the speaker puts greater emphasis or effort into their lesson preparation compared to the other person, aligning perfectly with the comparative nature of "than you." Thus, "I prepare my lesson more carefully than you" presents a clear and meaningful statement that demonstrates the intended comparison.