Suppose an Economy Produces Only Solar Panels and Coal

Suppose an economy produces only solar panels and coal. Between 2005 and 2015, the production possibilities curve (PPC) for this economy shifted out as characterized in the figure below.
Which of the following statements best describes the shift in the PPC between 2005 and 2015?

A) Increases in the supply of inputs affected both the coal and solar panel industries equally.
B) Technological innovation had a larger positive effect on the production of solar panels.
C) Productivity gains had a larger positive effect on the production of coal.
D) Productivity gains had equal effects on the production of solar panels and coal.