Wave interference
a. is a property of light
b. occurs when light and water interact
c. is a property of all waves

The answer is C. Wave interference is a property of all waves. For example, light waves, radio waves, surface water waves, matter waves, acoustic waves, or gravity waves.

The correct answer is option is Option C, is a property of all waves

Explanation:

Wave interference is a physical phenomenon in which two waves meet each other when they travel through the same medium. Wave interfere in two ways

a)  Constructive Interference – In this the two waves cancel out each other as they have equal and opposite amplitude

b)Destructive Interference – In this the two waves add to each other as they travel in the same direction and the resulting wave has higher wavelength.  

the old price per ounce is c/4.

the new price per ounce is c/3.6.

the ratio of the old price to the new one is

(c/4)/(c/3.6) = (c/c)×(3.6/4) = 0.9 . . = 9/10 . . "nine tenths" in either form