The radar controller suspects that you are experiencing unlawful interference. What should he do to confirm this with an auto decoder unit? (with no mode A interpretation?)

Question 467, Air Law - ATPL - Airline Transport Pilot license

Switch from 7500 to 7700.

Switch from 7000 to 7500.

Switch from 7600 to 7700.

Switch from 7700 to STBY to test 7500.