The athlete, known for his unwavering determination and rigorous training regime, _______ prepared for the upcoming competition, _______ pushing his physical and mental limits to achieve peak performance.
Correct: A
The correct answer is 'diligently; thereby'. The adverb 'diligently' modifies 'prepared.' 'Thereby' clearly indicates cause and effect. The adjective 'diligent' is grammatically incorrect. While 'thus' is also correct in meaning, 'thereby' more directly highlights the consequence.