What principle was used to develop the geologic time scale?

Which of the following is an accurate description of the recent political history of the democratic republic of the congo? a. religious tensions have escalated into full-scale civil war a number of times since the belgians left the country in 1960. b. the political leader who gained power after the overthrow of a corrupt dictator was assassinated. c. the military leadership felt the country was stable enough, so they permitted democratic elections to take place. d. in 1990, a dictator seized and has held power ever since.