The correct answer is option 'C': Unstriated muscles.

Unstriated muscles, also known as smooth muscles, are responsible for the movement of food through the intestine. These muscles are found in the walls of the digestive tract, including the intestines. Unlike striated muscles, which are found in skeletal muscles and are under voluntary control, smooth muscles are involuntary and are not under conscious control.

Here is a detailed explanation of how the contraction of unstriated muscles helps in the movement of food through the intestine:

1. Peristalsis: The movement of food through the digestive tract is mainly achieved by a process called peristalsis. Peristalsis is a wave-like contraction and relaxation of the smooth muscles in the walls of the intestines.

2. Circular and longitudinal muscles: The walls of the intestines have two layers of smooth muscles: circular muscles and longitudinal muscles. The circular muscles encircle the intestine, while the longitudinal muscles run along the length of the intestine.

3. Contraction and relaxation: When food enters the intestine, the circular muscles contract, causing the diameter of the intestine to decrease. This contraction creates a squeezing force on the food, pushing it forward. At the same time, the longitudinal muscles contract, shortening the length of the intestine.

4. Wave-like movement: As the circular muscles contract behind the food, the longitudinal muscles relax in front of it, creating a wave-like movement that propels the food forward. This coordinated contraction and relaxation of the smooth muscles continue along the entire length of the intestine, pushing the food towards the rectum.

5. Sphincter muscles: In addition to the peristaltic movement, there are also sphincter muscles present at various points in the digestive tract. These muscles act as valves, controlling the flow of food between different parts of the digestive system. The contraction and relaxation of these muscles help to regulate the movement of food through the intestines.

In conclusion, the contraction of unstriated muscles, also known as smooth muscles, is responsible for the movement of food through the intestines. These muscles undergo peristalsis, a wave-like contraction and relaxation, to propel the food forward. The coordinated contraction of circular and longitudinal muscles creates a squeezing and wave-like movement, respectively, that helps in the smooth passage of food through the intestines.