Rennin acts on
(a) milk changing casein into calcium paracaseinate at 7.2 - 8.2 pH
(b) protein in stomach
(c) fat in intestine
(d) milk changing casein into calcium paracaseinate at 1-3 pH
(d) Stomach secretes gastric juice pH [1-3.5] which contains prorennin secreted by the zymogen cells. Inactive prorennin is converted into rennin by HCl. Rennin acts on casein, a protein milk changing it into calcium paracaseinate, it is known as curdling of milk.