Which have scientists learned from studying seismic waves that travel through earth’s interior? a. the crust of earth is liquid. b. the layers of the earth increase in density as one moves toward the earth's center. c. there are no finite boundaries between the layers. they mesh into one another. d. the inner core of earth is liquid.

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?