Answer:
C. The dog, growling and snarling, snapped at me; I was so frightened that I ran.
Explanation:
In option C, the semicolon is correctly used to connect two independent clauses. The first clause is "The dog, growling and snarling, snapped at me," and the second clause is "I was so frightened that I ran." Both clauses are independent and could stand alone as separate sentences, so a semicolon is appropriate to join them together.
Option b would be correct if the semicolon was placed before "however."