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

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

Answer - A lower CPA may also have lower sales volume, reducing overall profit