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

Fact 2: Coral is the calcite shell of the coral animal.

Given the two facts above, answer the question "what forms large colonies in shallow tropical water?" with the following options: 
- Most plants
 - passenger pigeons
 - orchids
 - honeybees
 - calcite shells
 - trout
 - sharks
 - humans


 

     calcite shells    