Why Was Theodore Roosevelt Picked as William McKinley's Running Mate

Why was Theodore Roosevelt picked as William McKinley's running mate for the 1900 election?

A) Roosevelt was a master of the spoils system and was bribed into entering politics by his acquaintances in Big Business.
B) Roosevelt's calm and conservative approach to politics nicely balanced McKinley's more radical inclinations.
C) McKinley was secretly suffering from a fatal disease, and Republican leaders wanted Roosevelt to succeed him.
D) Roosevelt was a popular figure from his exploits in the Spanish-American War and had been a strong public supporter of McKinley.
E) Roosevelt's strict focus on domestic affairs as opposed to world affairs was viewed as necessary after the Spanish-American War.