Which of the following is the longest division of geologic time?
a. period
b. era
c. year
d. epoch

The answer is option B "era." A era can be up to several millions of years. It isn't period because period can be days to years, it isn't years because it's only one year, wouldn't be option D either because a epoch is up to three million years.

Hope this helps.

the objects have the same charge.