Question

His speech had become increasingly slurred (state the word class of increasingly)

Answer 1

increasingly is adverb clause of manner

Answer 2

Explanation:

Here Increasingly' has been used  as an adverb. An adverb can be used to change an adjective, clause, sentence, verb, determiner or preposition. They are usually used to describe a place, frequency, level of certainty, manner, time or degree, etc. They are the part of the speech and you can also add an adverb to change the parts of a speech.