Fact 1: Corals form large colonies in shallow tropical water.

Fact 2: Huge colonies of hard corals form coral reefs .

Given the two facts above, answer the question "What forms in shallow tropical water?" with the following options: 
- ocean
 - romance
 - bushes
 - ferns
 - reefs
 - bamboo
 - fossils
 - snorkelling


 

     reefs    