What is a variety of living things in an area?

What are the headings of a data table

What do isotopes of uranium have the same number of? what do they have a different number of? a) same number of protons; different number of electrons b) same number of protons; different number of neutrons c) same number of electrons; different number of protons d) same number of neutrons; different number of protons

Which of the following is the earliest era of earth's geologic time scale? cenozoic mesozoic precambrian paleozoic