To answer this question, let's go through each option:
Option A) Assigning existing controls to the array - This option is correct because you can populate an array of controls by assigning existing controls to it. This means that you can take controls that already exist and add them to the array.
Option B) Creating controls and assigning them to the array - This option is correct because you can also populate an array of controls by creating new controls and assigning them to the array. This means that you can create controls dynamically and add them to the array.
Option C) Borrowing controls that will automatically assign them to the array - This option is incorrect because there is no mention of "borrowing" controls in the question. Additionally, controls cannot be automatically assigned to an array without explicit assignment.
Option D) Both a and b - This option is correct because both assigning existing controls and creating controls and assigning them to the array are valid ways to populate an array of controls.
Option E) All of the above - This option is incorrect because option C is incorrect. Controls cannot be automatically assigned to an array without explicit assignment.
Therefore, the correct answer is D) Both a and b. This option is correct because you can populate an array of controls by both assigning existing controls to the array and creating controls and assigning them to the array.