At 10,000 feet elevation (atmospheric pressure is 520 mm Hg), oxygen 100 mL/min is bubbled through a vaporizer containing an anesthetic with a vapor pressure of 260 mmHg. This mixture is added to a fresh gas flow of 5 L/min. The delivered anesthetic concentration is:

A) 0.25%
B) 0.5%
C) 1%
D) 2%