Answer:
C. Formidable
Step-by-step explanation:
The word that best completes the given sentence is formidable. When someone is formidable, it means that they inspire fear or respect by being impressively large, powerful, intense, or capable. This word is commonly used in the phrase formidable opponent.
The word interesting means holding or catching someone's attention. It does not perfectly fit the context, and the phrase interesting in (something) is not used.
Enormous means very large in size, quantity, or extent. Skills are not often described as enormous, and the phrase enormous in (something) is also not used.
Tedious means too long, slow, or dull. This word is the worst option.
Thus, the correct answer is C.