With reference to human body systems and their functions, consider the following statements:

1. 1. In the human digestive system, the liver is the largest gland in the body, which secretes bile, although it does not contain any digestive enzymes, yet it plays an important role in the emulsification of fats.
2. 2. In the human respiratory system, the exchange of gases takes place through the thin membrane of the alveoli located inside the lungs by the process of diffusion, and oxygen is transported in the blood mainly in the form of 'oxyhemoglobin' with hemoglobin.
3. 3. In the human circulatory system, the right atrium and right ventricle of the heart receive deoxygenated (carbon dioxide-rich) blood and pump it to the lungs, while the left atrium and left ventricle circulate oxygenated blood to various parts of the body.
4. 4. In the human excretory system, the process of urine formation in the nephron is completed through three stages—glomerular filtration, selective reabsorption, and tubular secretion.

Which of the above statement(s) is/are completely true?