Why do aldehydes undergo nucleophilic addition reactions while esters undergo nucleophilic acyl substitution reactions? A: The carbonyl carbon of an ester is more electrophilic than that of an aldehyde. B: Aldehydes are more sterically hindered than esters. C: Once the nucleophile adds to an aldehyde, the tetrahedral intermediate is too sterically hindered to eliminate one of the attached groups. D: Once the nucleophile adds to an aldehyde, neither H− nor R− can be eliminated since they are strongly basic.