Which precaution was implemented due to the actions of the shoe bomber?

The correct answer highlights the introduction of shoe control checks at airports, which was a direct response to the shoe bomber incident in December 2001. This attack involved a man attempting to detonate explosives hidden in his shoes while aboard an aircraft. As a result, airport security protocols were revised to include procedures requiring passengers to remove their shoes during the screening process. This measure aims to ensure that no concealed dangerous items are missed during inspections, improving overall security on flights.

The other options, while related to security enhancements initiated in the years following various threats, do not specifically stem from the actions of the shoe bomber. Increased screening for electronics, limitations on liquid carry-ons, and full-body scanning were introduced for different reasons and incidents involving other forms of potential threats.