Answer:
Definition 4.
Having qualities that discourage approach due to extreme difficulty.
Explanation:
From the four different definitions, the one that states the meaning of the word "formidable" is Definition 4 (See attached image).
The word formidable is used in the context of the sentence,
"To the tired track runner, the formidable last hurdle looked twice as large as it actually was"
Therefore, the meaning of the word according to the context is having qualities that discourage approach due to extreme difficulty because from the sentence, the tired track runner is looking at the last hurdle and seeing it as twice as large as it actually was.
