There is no underlined word.....
Answer:
Short Examples of Allusion
His opponent was looking for his Achilles' heel to beat him. The property tycoon named his housing society Eden Garden. The decision of the apex court would certainly open Pandora's Box. His best friend now considered him Brutus due to his recent betrayal.
Many of the runners ____ incredibly fast.
The subject is "many" and many is plural.
Has would be wrong because you need a linking verb (the predicate is an adjective)
"Is" would be wrong because the subject is plural and "is" corresponds to a singular subject.
"Was" is incorrect because "was" corresponds to a singular noun.
Therefore "are" would be correct because it is a linking verb that corresponds to a plural noun.