Which relation is a function?

A. (-2,-12),(-2,0),(-2,4),(-2,11)

B. (8, 1),(4, 1),(0, 1),(-15, 1)

C. (0, 1),(0, 2),(1, 2),(1, 3)

D.(-4,-6),(-3,-2),(1,-2),(1, 0)

answer: 4  

the square root of 16 is 4. it is a very simple mathematic concept. a square root when a number multiplied by itself will result in a number. here, the number 16 comes when 4 is multiplied by 4. hence the square root of 16 is 4. you can always figure out a square root by the inverse operation of squaring.