Final answer:
The correct punctuation mark that should be used instead of the semicolon after STATE is a comma.
Step-by-step explanation:
The correct punctuation mark that should be used instead of the semicolon after STATE is a comma.
In the given sentence, the semicolon is used incorrectly because it separates two independent clauses, but the second clause does not make sense on its own. To fix this, a comma should be used to separate the two clauses.
So, the correct sentence would be: 'One key inventor in the United States was Robert Fulton, who brought affordable steamboat travel to New York State; another was Cyrus Hall McCormick, who invented the indispensable reaper.'