Given a scientific question and its correct answer, generate supporting facts for the answer. This supporting fact can be an explanation for the answer to the given question.

Question: Four electron groups orient themselves into what shape that has four faces? Answer: tetrahedron
Four electron groups orient themselves in the shape of a tetrahedron.

Question: Both endocytosis and ______ are active transport processes. Answer: exocytosis
Both endocytosis and exocytosis are active transport processes.

Question: What is an isotope that is radioactive called? Answer: radioisotopes
Many elements have one or more isotopes that are radioactive. These isotopes are called radioisotopes. An example of a radioisotope is carbon-14.