16.  FALSE
17. TRUE
18. FALSE
19. TRUE
20.  TRUE
        
             
        
        
        
B. This is because the Hydrogen and Oxygen need balanced out.
Current-
C-1            |        C-1
H-4            |         H-2
O-2            |         O-3
Adding a coefficient of 2 before oxygen in the reactants and H2O in the products would balance this equation
<span>CH4 + 2O2 → CO2 + 2H2O</span>
C-1            |        C-1
H-4            |         H-4
O-4            |        O-4
        
             
        
        
        
Answer:
New experimental methods 
Technological inventions
Explanation:
A scientific theory is usually not based on speculation. Scientific theories must have a solid empirical basis. 
However, experimental methods are limited to the caliber of equipments available at the time in which a theory is formulated. With advancing years, more technological sophistication leads to the invention of new instruments and ultimately, the development of new experimental methods.
These innovations are likely to alter existing scientific theories as new evidences emerge, hence the answer.
 
        
                    
             
        
        
        
Not sure but it might be A or B