Sulfur Dioxide Gas Reacts with Oxygen Gas to Form Sulfur

Sulfur dioxide gas reacts with oxygen gas to form sulfur trioxide gas. Based on the initial reaction mixture, what should be present after the reaction occurs?

A) 2 molecules of sulfur trioxide, and 2 molecules of sulfur dioxide
B) 4 molecules of sulfur trioxide, and 1 molecule of oxygen
C) 3 molecules of sulfur trioxide, and 1 molecule of oxygen
D) 3 molecules of sulfur trioxide, and 1 molecule of sulfur dioxide
E) 4 molecules of sulfur trioxide