Contour lines are lines that signifies the elevation on a mountain or hill
        
                    
             
        
        
        
Answer:
Hydrochloric and Hydrofluoric Acids.
 
        
             
        
        
        
In Physics, 'work' has a very clear definition:
It's (strength of a force) times (distance through which the force acts).
'Work' has the units of Energy.
If you push against a shopping cart with 30 newtons of force, and 
you keep pushing while the cart moves 4 meters, then you have 
done (30 x 4) = 120 newton-meters of work = 120 "Joules".