Oxidation of toluene to benzaldehyde can be easily carried out with which of the following reagents?
\( \mathrm{CrO_3} \) / acetic acid, \( \mathrm{H_3O^+} \)
\( \mathrm{CrO_3} \) / acetic anhydride, \( \mathrm{H_3O^+} \)
\( \mathrm{KMnO_4} \) / \( \mathrm{HCl} \), \( \mathrm{H_3O^+} \)
\( \mathrm{CO} \) / \( \mathrm{HCl} \), anhydrous \( \mathrm{AlCl_3} \)
