The correct option is B A- Lactic acid, B- Vitamin B12
Milk is inoculated with a small amount of curd having millions of Lactobacillus commonly called lactic acid bacteria (LAB).
Curd has more nutritional value compared to milk, for increasing the quantity of vitamin B12. Vitamin B12 is a water soluble vitamin involved in protein metabolism and blood functions. Curd is easily digestible and can be consumed by the lactose intolerant people as the raw form of lactose gets converted into its constituent
A small amount of curd full of lactic acid bacteria (LAB), as a starter, is added to the fresh milk. At suitable temperature LAB starts multiplying, with an increase in the number of bacteria the lactic acid in the milk also increases making the environment acidic resulting in coagulation of milk protein into curd.