Which of the following reactions converts >C=O to >CH_2 ? (A)...

Rosenmund's reaction is used for the partial reduction of acid chlorides to aldehydes using $\text{H}_2$ and $\text{Pd/BaSO}_4$.

Aldol condensation involves the reaction of two molecules of aldehydes or ketones having at least one $\alpha$-hydrogen in the presence of a dilute base to form $\beta$-hydroxy aldehydes or ketones, which upon heating give $\alpha,\beta$-unsaturated carbonyl compounds.

Clemmensen's reduction involves the reduction of aldehydes and ketones to their corresponding alkanes ($>\text{C=O} \rightarrow >\text{CH}_2$) using zinc amalgam ($\text{Zn-Hg}$) and concentrated $\text{HCl}$.

Wolf-Kishner reduction involves the reduction of aldehydes and ketones to their corresponding alkanes ($>\text{C=O} \rightarrow >\text{CH}_2$) using hydrazine ($\text{NH}_2\text{NH}_2$) followed by heating with a strong base like $\text{KOH}$ or $\text{NaOH}$ in a high-boiling solvent such as ethylene glycol.

Thus, both Clemmensen's reduction and Wolf-Kishner reduction convert $>\text{C=O}$ to $>\text{CH}_2$.

Answer: (C) and (D) only.