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