A carbonyl compound $\text{'}\mathrm{A}\text{'}$ reacts with hydrogen cyanide to form a cyanohydrin $\text{'}\mathrm{B}\text{'}$ which on hydrolysis gives an optically active alpha hydroxy acid $\text{'}\mathrm{C}\text{'}. \text{'}\mathrm{A}\text{'}$ gives a positive iodoform test $\text{'}\mathrm{A}\text{'}, \text{'}\mathrm{B}\text{'}$ and $\text{'}\mathrm{C}\text{'}$ are