A quadratic function is a function in the form,
Option A is a quadratic function,
Option B, is not a quadratic function because it is not the form of the equation written above and also,
Option C is also not a quadratic function because it has the highest degree of x to be 3.
In option D the function is given by the function is defined by
This implies that the function in option D is a quadratic function
Option E is not a quadratic function