If the aircraft's radio fails, what is the recommended procedure when landing at a controlled airport
a. Use alternative means of communication such as a handheld radio or signaling to the control tower.
b. Follow standard arrival and landing procedures and be prepared for light gun signals if available.
c. Monitor the frequency for any instructions from the control tower and be prepared to follow visual signals from the tower.
d. Declare an emergency and follow the emergency landing procedures as directed by the control tower.