The surgeon, known for his steady hand and precise technique, _______ performed the complex operation, _______ saving the patient's life and restoring his health.
Correct: A
The correct answer is 'skillfully; thereby'. Skillfully modifies performed. Thereby indicates the result of the operation. Skillful is not the correct modifier for a verb. Thus can work, but thereby is more clear as it directly states how the saving is being performed.