This Graph Shows the Cost Functions of Moe's Mushroom Gathering

This graph shows the cost functions of Moe's mushroom gathering business,which is perfectly competitive.
The curve labeled A is upward sloping because

A) there are high fixed costs.
B) the first bushels of mushrooms are the easiest to find,but Moe has to really hunt to find additional mushrooms.
C) increased demand for mushrooms has increased quantity supplied.
D) supply has shifted to the left.