The Supply Curve Slopes Up and to the Right Because

The supply curve slopes up and to the right because

A) due to constant opportunity costs, producers feel that people will buy more if they charge a higher price.
B) due to efficiencies, producers feel that people will buy more if they charge a higher price.
C) due to increasing opportunity costs, producers must charge more to produce additional units in order to cover their costs.
D) The supply curve actually slopes down and to the right.