Which of the following can exist as a pair of stable geometrical isomers? (Treat $\mathrm{C}=\mathrm{N}$ and $\mathrm{N}=\mathrm{N}$ bonds as configurationally stable.)

A $\mathrm{C}=\mathrm{N}$ or $\mathrm{N}=\mathrm{N}$ bond is stereogenic when each end carries two different 'groups' (a lone pair counts as one). Acetaldoxime: carbon has $\mathrm{H}$/$\mathrm{CH}{}_3$, nitrogen has $\mathrm{OH}$/lone pair, so it is stereogenic. In $\mathrm{C}{}_6\mathrm{H}{}_5-\mathrm{N}=\mathrm{N}-\mathrm{CH}{}_3$ each nitrogen has one substituent and a lone pair, so cis and trans (E/Z) forms exist. Acetone oxime (two $\mathrm{CH}{}_3$) and formaldoxime (two $\mathrm{H}$) are not stereogenic. Correct: A and C.