Our elbow bends all the time, we bend it when we pick up things, when we eat, when we do mostly everything. Cows on the other hand dont pick up food with there feet, they use there mouths, and they probably only bend when they are walking.
All living organisms are made of only 20 different aminoacids- this is the correct answer! This means that the genetic code only codes for those 20 aminoacids (for example Glutamine and Lysine).
The 20 aminoacids that can form proteins are also called Proteinogenic amino acids.
The answer would be C. Digestive
The <em />circulatory system <em>circulates</em> the blood and lymph throughout the body. The excretory system <em>excretes</em> the body wastes.
B. tears , this is not a first line of defense
<span>C) the force of gravity</span>
