Study the following flow chart that shows curd formation from milk and select the correct option for $A$ and $B$.
Milk is incubated with curd
$\downarrow$
$LAB$ shows growth in milk
$\downarrow$
Production of .....$A$.....
$\downarrow$
Coagulation and digestion of milk protein
$\downarrow$
Improved nutritional quality by increased ....$B$....

• A
  $A-$citric acid; $B-$vitamin-$B_{12}$
• B
  $A-$lactic acid; $B-$vitamin-$B_{12}$
• C
  $A-$lactic acid; $B-$vitamin-$C$
• D
  $A-$citric acid; $B-$vitamin-$B_{2}$