Answer: The balanced equation for the given reaction is
.
Explanation:
A chemical equation which contains same number of atoms on both reactant and product side.
For example, 
Here, number of atoms on reactant side are as follows.
Number of atoms on product side are as follows.
To balance this equation, multiply
by 2 on reactant side and multiply
by 2. Hence, the equation will be re-written as follows.

Here, number of atoms on reactant side are as follows.
Number of atoms on product side are as follows.
Now, there are same number of atoms on both reactant and product side. So, this equation is balanced.
Thus, we can conclude that the balanced equation for the given reaction is
.
Answer:
The body has levels of organization that build on each other. Cells make up tissues, tissues make up organs, and organs make up organ systems. The function of an organ system depends on the integrated activity of its organs.
The answer is D, because "Animals without a backbone are invertebrates."