Answer:
The sentence would be as follows: After Robert Fulton invented the steamboat, he tried it out on the Hudson River.
Explanation:
Adverb clauses, also called adverbial clauses, are dependent clauses that function as adverbs. As they are dependent clauses, they must have a subordinating conjunction to connect them to the rest of the sentence.
A dependent clause is a group of words that can't stand on its own as a sentence because it does not represent a complete thought (2). They depend on the main clause to complete their meaning (3). In this case, the dependent clause (2) has been introduced by the subordinating conjunction <em>after, </em>adding information as regards the time in which the event took place.
1) After Robert Fulton invented the steamboat, he tried it out on the Hudson River.
2) * After Robert Fulton invented the steamboat
3) He tried it out on the Hudson River
