Sand is supplied to the california coastal region primarily by:
• (a)coastal erosion •
• (b)local biological activity •
• (c)rivers that flow from the sierra-nevada mountains
•(d)ocean floor upwelling

I think the correct answer would be A. Sand is supplied to the California coastal region primarily by coastal erosion. It is a type of erosion that removes sand, sediments through the action of the waves, tidal currents or high winds in a certain beach system. The, the sands that had been eroded are moved to the coastal region of California. 

Sequoia national park  /  inyo national forest, california, u.s. mount whitney is the tallest mountain in california, as well as the highest summit in the contiguous united states and thesierra nevada—with an elevation of 14,505 feet (4,421 m).

Amath expression is a collection of one or more terms, which are separated by the signs ( + , - , x , / ).example :   8+b8+b  or  a−3a−3in algebra, an equation is a mathematical statement with two expressions where, each expression is separated by an equal (=) sign. variables can be present on both the sides of the equality (=) sign and we use letters to denote such variables.example 1:   x=4+2x=4+2  , [here, we can observe that the variable is present only on one side of the equation].example 2:   2x+3=x+42x+3=x+4  , [here, we can observe that the variables are present on both side of the equation].