The answer to this is probably their ability to absorb heat. Oceans are great at absorbing heat from the sun and storing it. If they were bad at it, the heat would be trapped due to the greenhouse effect and the climate would become scorching hot. This way, oceans absorb large amounts of heat and effectively reduce the overall temperature of the world.
        
                    
             
        
        
        
C
5x < 30
Divide each side by 5 to find x
x < 6
The number line needs to show the x represents any number less than 6 (3, 5.5, -1, etc)
C is correct because there is an open circle around 6, and then an arrow pointing towards numbers smaller than 6. 
If x is less then or equal to six, you draw a filled in circle around six to show that x can be 6. 
Because x is less than 6 and not equal to 6, you draw an open circle to represent x can get very close to 6 (ex. 5.9, 5.999) but cannot equal 6. 
The line has to be pointing leftwards because the numbers are less then six in that direction. X can be any number smaller than 6, which is how by the leftward arrow