Audit Procedures Test of Controls

I have recently done this question
Q)Which of the following is Audit Procedures is a test of controls?
1.Checking that the total shown on the aged list of receivables has been correctly analysed.
2.Checking that approved sales orders indicate that reference was made to the aged listing.
3. Enquiring whether the aged listing is used as a basis for credit control decisions
4. Checking that the total of the nominal ledger receivables control account agrees to the
total shown by the aged listing.
The answer given was ‘2’ checking that the approved sales orders indicate that reference was made to the aged listing
Stating that reference should be evidenced by signature-checking for that signature is the controls test.
I dont understand what they mean by this as have never known for this to happen in the real world. If anything I would have said option 3 but even this is unlikely as if a customer were over their terms for payment or over their credit limit the account would be on hold and most systems would not allow an order to be processed.Have i misinterpreted what they are asking?