"A function is a special type of mathematical relationship between two variables, the input variable and the output variable, such that each element in the set of input values is assigned to exactly one element in the set of output values. While more than one input element in a function may be assigned to the same output value, a single input element cannot be assigned to more than one output element. For example, the relationship y=2x is a function that assigns each input element, x, to an output element, y, that is twice its value. When x=3, y will always be equal to 6. This means that for relationships that are functions, if you are given a specific value for the input variable, x, you can precisely identify its assigned output value. Alternatively, the relationship x2+y2=4 is not a function, because each input element is associated with both a positive and a negative output value. For example, when x = 0, both y = 2 and y = − 2 will make the equation true. This means each input element is not assigned to exactly one output value. While this mathematical relationship is important—it defines a circle with radius 2 units—it is not classified as a function."
Why did the author begin the last paragraph with the word “Alternatively”?
A) To indicate that the paragraph will present a contrast to the previous one
B) To signal that the paragraph will give another example of a function
C) To suggest that functions are more important than nonfunctions
D) To reveal that the tone of the text is becoming more serious