Answer:The Cell Membrane. All living cells and many of the tiny organelles internal to cells are bounded by thin membranes. These membranes are composed primarily of phospholipids and proteins and are typically described as phospholipid bi-layers.
From this we can conclude that the human digestive system does not produce enzymes that can break down cellulose. The correct option among all the options that are given in the question is the fourth option or the last option. I hope that this is the answer that has come to your desired help.
The external ear structure is called the Pinna.
The Pinna helps to channel sound waves into the ear.
Many animals have the ability to move their pinna towards the direction of sound.
I have attached an image of a dog's ear to show you the external structure called the Pinna.
I hope this helps! I'm happy to answer any other questions you might have :)
[Image sourced from: https://www.msdvetmanual.com/dog-owners/ear-disorders-of-dogs/ear-structure-and-function-in-dogs]
When you spin around, you lose balance because of fluid spinning around in the C) semicircular canals.