A lower CPA does not necessarily indicate higher profit. Why?

81) A lower CPA does not necessarily indicate higher profit. Why?

  A)  A lower CPA may be due to changes in CPC bidding
  B)  A lower CPA may also have lower sales volume, reducing overall profit
  C)  A lower CPA may be due to additions in negative keywords

  D)  A lower CPA may be due to changes in network distribution