To answer this question, the user needs to have knowledge about the concept of using an external file.

Option A is incorrect because it does not fully explain the benefit of using an external file. While it is true that the main program can reference the record area of the file even if it does not have input or output statements, this is not the main benefit of using an external file.

Option B is incorrect because it is a specific benefit that applies only to subprograms. It does not explain the general benefit of using an external file.

Option C is incorrect because it is too general. It does not explain the specific benefit of using an external file.

Option D is the correct answer because it includes all the benefits of using an external file. These include the ability for the main program to access the record area of the file, the ability for subprograms to control specific input or output functions, and the fact that multiple programs can have access to the same file.

Therefore, the answer is: D. (4) All the above.