To produce butanone, which of the following should be reacted with Na₂Cr₂O₇(aq), H₂SO₄(aq)?
a. CH₃CH₂CH₂CH₂OH
b. (CH₃)₂CHCHO
c. CH₃CH₂CH(COOH)CH₃
d. CH₃CH₂CH(OH)CH₃
e. CH₃CH₂CH(CH₂OH)CH₃