What are three properties of electromagnetic waves?
a. they travel slower than the speed of light, they include visible light waves, and they can transfer energy through empty space.
b. they need matter through which to travel, they travel at the speed of light, and they include visible light waves.
c. they travel at the speed of light, they include ultraviolet waves, and they can transfer energy through empty space.
d. they include ultraviolet waves, they need matter through which to travel, and they travel slower than the speed of light.

You have two photos of a person walking. one shows the person at the corner of third and main streets, the other shows the person at the corner of tenth and main streets. there are lampposts at every corner in this town, and the first picture shows it to be 10: 32: 00 exactly. the second picture shows it to be 10: 49: 30. you know three facts: (1) all of the clocks are synchronized; (2) there are exactly 12 equal-sized blocks per kilometer in this town; and (3) the streets that cross main in this area are numbered consecutively, with no interruptions. what is the person’s average speed in kilometers per hour?