Hi Mr. Irons,
As temperature increases at a given FL, Air Density decreases.
The Fan (N1) produces most of the thrust. The lower the density, the less power is needed to rotate it at the same N1 therefore fuel flow decreases - SFC has decreased. With the same IAS, TAS has increased because of the lower density.
I'd have gone for A.
That's why we fly as high as we can (low air density) for best TAS & fuel economy.