Adverbs are demonstrated as the words that function to modify or provide description about an adjective, verb, adverb, or other kinds of words, clauses, or phrases. As per the question, the adverb that is mentioned in the given sentence would be 'too' as it qualifies the adjective 'close' in the sentence. The adverb 'too' is usually employed before adjectives to qualify/describe the adjectives without nouns as provided in the given sentence('close' is followed by a preposition not noun).
Salamanders can regrow entire limbs and regenerate parts of major organs, an ability that relies on their immune systems, research now shows. ... They then wiped out some or all of the macrophage cells to determine whether these cells were essential for regrowing the limbs.
