Choose the sentence that contains the grammatical error of a fragment, a comma splice, or a fused sentence.

1) The current was too swift he could not swim to shore alone.
2) The book was a best seller, but the total sales fell short of the author's
previous novel's sales.
3)
Our country observed its bicentennial in 1976; our city observed its twentieth
birthday the same year.
4) Since enrollment increased significantly over the previous year, the college
installed several temporary buildings.