In the Lungs, the Respiratory Membrane Separates Tiny (Spherical) Sacs $\times$

In the lungs, the respiratory membrane separates tiny (spherical) sacs of air called alveoli (pressure 1.0 $\times$ 10⁵ N/m², temperature 310 K, and radius 0.11 mm) . The air in the lungs contains 14% oxygen. The number of oxygen molecules in one sac is

A) 9.3 $\times$ 10¹⁴.
B) 4.7 $\times$ 10¹⁴.
C) 1.3 $\times$ 10¹⁴.
D) 1.8 $\times$ 10¹³.
E) 9.0 $\times$ 10¹².