Answer:
Fine focus.
Explanation:
If you're referencing a microscope, then it would be fine focus. Coarse focus is a basic focus used to properly see a specimen, while fine focus enhance clarity and precision. To use both, you have to gently twist a knob until you can see the specimen at a desired clarity.
Here's a reference image if you need it, it's labeled all the parts of a microscope.
The answer is Coral extinction. Extinction is a term that is a result to the excessive lost of organism. Coral reefs are from the shallow water corals that gro fast enough to build this huge population of reefs. They are from the single celled algae that were photosynthesized and passed to some of the food and give nutrients to algae.