For the following molecule, choose two constitutional isomers that contain different functional groups: CH₃CH₂COOH.
a) CH₃CH₂COOH and CH₃CHO
b) CH₃CH₂COOH and CH₃COCH₃
c) CH₃CH₂COOH and CH₃CH₂OH
d) CH₃CH₂COOH and CH₃COOH