Read the passage. The eastern diamondback rattlesnake is the largest poisonous snake in the United States. Eastern diamondbacks grow as long as eight feet, with the average length often being two to six feet. Like many other rattlesnakes, they frequently make a buzzing sound with the rattles on their tails when they feel threatened. They usually live in the southeastern United States and eat rabbits, rodents, and birds.

Which is the underlined adverb modifying?

The underlined adverb is “frequently”