Step 1 : Introduction to the question "2. Since 1957, US military radio operators have used a standard phonetic alphabet so that letters could be understood more easily over radio transmissions. This current phonetic alphabet uses which words for X and Y, respectively?"
...1. X-ray and Yoke 2. X-ray and Yankee 3. Xylophone and Yahoo 4. Xenon and Yesterday X-Ray has been standard since 1913. Yoke was changed to Yankee in 1957.