Final answer:
Examples of hard corals include Elkhorn, Staghorn, Fire, and Star corals, whereas Sea Fans are soft corals, which makes option 4 incorrect.
Step-by-step explanation:
Two examples of hard coral reefs are: 1) Elkhorn and Staghorn 2) Fire and Star 3) Sea Fan and Brain 4) All answers are correct. When we look at these options, Elkhorn and Staghorn corals are indeed types of hard corals, known for their rigid calcium carbonate skeletons. However, the Sea Fan is actually a type of soft coral, indicating that not all the options listed portray hard corals. Therefore, the correct answer to this question is that examples of hard coral reefs include Elkhorn and Staghorn, and Fire and Star corals, making option 4 incorrect.