An element may have more than one isotope if the atoms have different numbers of A electrons.
B neutrons.
C positrons.
D protons.

What type of organism is a one-celled organism that functions as a single unit? a. bi-celled b. single-celled c. pre-celled d. multi-celled

Which event would lead to primary succession of a forest?

How much time has elapsed from the very beginning of "the memior of the conquistador bernal diaz del castillo" to the end? a. castillo's whole life b. a quarter of an hour c. a few weeks d. a decade