Correct option is A
Bread is prepared from dough which is fermented using Baker's yeast (Saccharomyces cerevisiae). Examples of acid producers are Aspergillus niger (a fungus) of citric acid, Acetobacter aceti (a bacterium) of acetic acid; Clostridium butylicum (a bacterium) of butyric acid and Lactobacillus (a bacterium) of lactic acid.