Which of the following is helpful in preventing disease-causing microbes in the stomach?

Which of the following is responsible for the conversion of milk into curd?

The dough used for making dosa and idli is fermented by which organisms,and what causes it to appear puffed up?

Which of the following food items are produced through fermentation by the microorganisms?
$(I)$ Idli $(II)$ Dosa
$(III)$ Toddy $(IV)$ Cheese

$P$ - Statement: Humans consume milk as a food item.
$Q$ - Statement: Milk is used to produce curd,butter,cheese,sweets,etc.

Which gas is primarily produced by microbes during the fermentation of dough,cheese making,and the production of beverages?