Answer:
The muscularis externa layer
Explanation:
The muscularis externa layer has three layers of muscle. An innner oblique layer , a middle circular and an external longitudinal layer. The contraction of these muscle layers help to break up the food mechanically.
I'm pretty sure it's false and that it is supposed to measure how you can do individually.
A triscupid valve has 3 and the biscuspid valve has two
The answer is A. physical stress.