In Bt cotton ,Bt toxin exist as inactive protoxins but after insect ingestion it is converted into an active form of toxin, why ?

Due to the basic pH of the gut . Due to the acidic pH of the gut . Due to the acidic pH of the intestine . Due to the alkaline pH of the gut .

Due to the alkaline pH of the gut .

The Bt toxin protein exist as inactive protoxins but once an insect ingest the inactive toxin, it is converted into an active form of toxin due to the alkaline pH of the gut which solubilise the crystals.