Most enzymes in living things are made up of what?
a. carbohydrates
b. nucleic acid
c. lipids
d. proteins

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