The answer would be D. milk turning sour! What happens when milk goes sour is it<span> ferment lactose at room temperature and which turns it into lactic acid. More acid means more hydrogen ions, a lower pH and a </span>sour<span> taste. Lower pH change the structure of proteins like casein, which gives </span>milk<span> its whiteness, so it curdles into clumps called curds! It's pretty gross!</span>
