Step 1: Read the question.
We must find what the main aim of education is to develop.
Step 2: Recall the holistic view.
Education seeks the all-round growth of an individual, not just one trait.
Step 3: Test option A (Knowledge).
Knowledge is only one part of development, so it is too narrow.
Step 4: Test option B (Body).
Physical growth alone misses mental and emotional growth, so it is partial.
Step 5: Test option D (Intelligence).
Intelligence is again just one dimension, so it is incomplete.
Step 6: Confirm option C (Personality).
Personality integrates cognitive, emotional, social, and physical development, making it the broadest aim.
Step 7: Conclude.
Hence education mainly develops personality.
\[ \boxed{\text{C. Personality}} \]