How is a blue hole different from a cave? a. A blue hole is always underwater. b. Caves usually have two sinkholes. c. Caves are inland, but blue holes are not. 2. What makes blue holes dangerous for divers? a. The guidelines are often not long enough to reach deep into the hole. b. There is poisonous gas at the top of the hole and darkness below. c. Bacteria grow between the fresh water and salt water layers. 3. What is astrobiology? a. the study of the location of stars in the universe b. the study of living things on Earth and other planets c. the study of creatures that don’t need oxygen to live 4. What does the phrase "habitable environments off Earth" mean? a. locations on the ocean’s surface to build floating cities b. caves on Jupiter’s moon where bacteria might live c. places on other planets where humans could live 5. What is special about the creatures that live in blue holes? a. Like most other living things, they need oxygen and sunlight. b. It’s possible they are the same as they were millions of years ago. c. They are closely related to creatures in other parts of the universe. 6. What does Kenny Broad think about exploring blue holes? a. It's worth the risk. b. It's extremely dark. c. It's too difficult.