Answer: Option D, composition.
Explanation:
In a function f(x) = y
x is the input, and the set of the possible values of x is called the domain.
y is the output, and the possible values of y is called the range.
Now, if we have two functions:
f(x) = y
g(x) = y.
we can define the composition of functions as: using the output of one function as the input of the other function, we can write this as:
f( g(x)) or fog(x)
In words, first we evaluate the function g in the point x, and the output of that is used as the input for the function f.
Then, the correct option here is D, composition.