Answer:option D.
Thickening of the circular layer of muscularis that controls movement of materials through the GI tract.
Step-by-step explanation:
Sphincter are circular muscles that control the opening and closing of body parts. Their main function is to control the movement of materials or fluid in the body.
There are five sphincter of the digestive system and they are;
Pyloric sphincter.
The lower oesophageal sphincter.
Ilocecal sphincter
Internal sphincter
External sphincter.
All this sphincter function to control the passage or movement of materials through the GI tracts.