Which of the following may explain the failure to observe Population III stars? 1. We do not expect to observe Population III stars because essentially pure hydrogen and helium stars never formed. 2. The surfaces of Population III stars were contaminated by remnants of massive stars. 3. The first stars to be formed in the young Milky Way were very massive and therefore short-lived and the surfaces of Population III stars were contaminated by remnants of massive stars are the best answers. 4. Answers 1, 2, and 3 5. Answers 2 and 3 are the only acceptable explanations.