I think they test ideas about chemical evolution by doing experiments. Hope this helps
Explanation:
The word BOOK; is made up of 4 letters and each actually represents the symbol of an element.
An element is a distinct substance that cannot be split-up into simpler substances.
B - Boron
O - Oxygen
O - Oxygen
K - Potassium
We can see that the word BOOK shows us elements boron, oxygen, oxygen and potassium.
Setting up the equation, you get
Therefore, the equation is 
A standard of measurement system is important because it allows scientists to compare data and communicate with each other about their results.
<span> A pure substance is a sample of </span>matter<span> with both definite and constant composition with distinct </span>chemical properties<span>. To avoid confusion, in chemistry a pure substance is often referred to as a "chemical substance".</span>
