Two volatile liquids (A and B) form an ideal mixture at 300.0K which just begins to boil at a pressure of 0.3000 atm. The vapor pressure of pure component A is 0.5000 atm and the vapor pressure of pure component B is 0.2000 atm, both at 300.0K. The closest value to the mole fraction of component A in the mixture is:
A. 0.40
B. 0.20
C. 0.33
D. 0.66
E. 0.80