Which of the following statements is true about protein digestion?

- Saliva does not contain proteolytic enzyme; protein digestion begins in the stomach by the action of pepsin. - Trypsinogen is conveed to trypsin by the action of enterokinase in duodenum. - Trypsin and chymotrypsin are endopeptidases; carboxypeptidase and aminopeptidase are exopeptidases. - Of the total protein digestion, 10%-20% occurs by the action of pepsin.