In the given sentence, identify the part of speech of the underlined word: 'I should try to probe into the soul of man through his art.'

Noun, Verb, Adjective, and Adverb are categories of word classes known as:

Identify the part of speech of the word 'extremely' in the sentence: 'Unlike previous telescopes, Webb operates at extremely low temperatures...'

Identify the part of speech of the word 'merely' in the sentence: 'Culture is not merely found in grand monuments or ancient artifacts...'