Which of the Following Is True for a Competitive Firm

Which of the following is true for a competitive firm operating in an input market cartel?

A) The individual firm's demand curve for the input is downward sloping when it acts alone.
B) The individual firm's supply curve is horizontal when it acts alone and upward sloping with coordinated hiring.
C) The individual firm's supply curve is upward sloping when the firm acts alone but horizontal otherwise.
D) The individual firm's supply curve is horizontal when it acts alone and downward sloping with coordinated hiring.