Because if you change two things then you do not know which one has affected or altered the dependent variable. if you only change one then you know what exactly changed and why
10g
Explanation:
Box 1, Mass of A = 10g
Box 2, Mass of B = 5g
Box 3, = 1A + 1B
Unknown:
Mass of B that would combine with mass of 20g of A
Solution:
Mass ratio of A to B:
= mass ratio
= mass ratio
The mass ratio of A to B = 2: 1
Now, number of B that will combine with 20g of A;
= mass ratio
= 
Mass of B = 10g
10g of B would combine with 20g of A
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Answer:
fossil
Explanation:
the dead organism is called a fossil i think