Answer:
The answer is letter a. Conjunctive adverb.
Explanation:
Adverbs are <em>words that modify a verb, an an adjective or another adverb.</em> It can also be used to modify a clause or a sentence.
In the example sentence above, "Andrew Carnegie was a poor immigrant; <u>however,</u> he later became a millionaire in the steel business," "however" functions as a<em> "conjunctive adverb."</em>
Conjunctive adverbs are adverbs that are used to connect two independent clauses (can stand alone) together. Examples of these are: <em>therefore, otherwise, next, however, nevertheless, then, finally, etc. </em>
Going back to the sentence above, the two independent/main clauses are: <em>"Andrew Carnegie was a poor immigrant"</em> and <em>"he later became a millionaire in the steel business."</em>