How Did the World's Countries Solve the Problem That Mean

Multiple Choice

How did the world's countries solve the problem that mean solar time varies continuously as a traveler's longitude changes?

A) they outlawed traveling long distances
B) they offered a reward and thus helped spur the invention of clocks and watches that can change the time they keep as you change longitude
C) an international convention adopted a single time zone for the entire world, so we can all be on the same time
D) the world was divided into 24 time zones, with all communities within a time zone keeping the same mean standard time
E) you can't fool me, this problem has not been solved yet