Answer the following question given this paragraph: 

The carbonyl group, a carbon-to-oxygen double bond, is the defining feature ofaldehydes and ketones. In aldehydes at least one bond on the carbonyl group is a carbon-to-hydrogen bond; in ketones, both available bonds on the carbonyl carbon atom are carbon-to-carbon bonds. Aldehydes are synthesized by the oxidation of primary alcohols. The aldehyde can be further oxidized to a carboxylic acid. Ketones are prepared by the oxidation of secondary alcohols. Mild oxidizing agents oxidize aldehydes to carboxylic acids. Ketones are not oxidized by these reagents. A thiol is a compound with an SH functional group.


Q: What are prepared by the oxidation of secondary alcohols?


A:
ketones