Serous fluid reduces friction:

between the visceral and parietal layers of serous membranes

in movable joints such as the knee

inside the lungs

around the brain

as food is chewed

The correct answer is A. Between the visceral and parietal layers of serous membranes

Explanation:

Serous fluid is a type of pale yellow fluid similar to mucus that is secreted by certain membranes to reduce friction in body cavities. This can be found on different organs in the body including the digestive system, for example in the peritoneum that encloses multiple organs in the abdomen. Additionally, serious fluid develops between two main layers: the visceral layer that covers the organs and the parietal layer that follows the visceral layer. According to this, serous fluid reduces friction "between the visceral and parietal layers of serous membranes".