Question

which kind of adverb extremely is​

Answer 1

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Adverb of Degree.

Answer 2

ᴀᴅᴠᴇʀʙ ᴏғ ᴅᴇɢʀᴇᴇ

Adverbs of degree are usually placed before the adjective, adverb, or verbthat they modify, although there are some exceptions.