coral reefs are amazing underwater worlds. they cover about 186,000 square miles of ocean floor. they mostly exist in the warmest parts of the world. this is because coral reefs develop in shallow, warm water, usually near land and mostly in the tropics. coral reefs prefer temperatures between 70 and 85 degrees fahrenheit. this is why they are found off the coasts of africa, india, australia, and brazil. coral reefs closest to us are found off the coast of florida.

2coral reefs are made up of groups of sea animals called coral polyps. these animals attach to each other and work together to keep the water safe for the plants and animals that live there. their hard skeletons remain when they are no longer alive. the stony structures they form provide protection and shelter for many different kinds of plants and fish.

3fish, clams, sponges, sharks, and sea turtles are only a few of the thousands of creatures that call coral reefs their home. many of the plants and fish that live in coral reefs depend on one another to live and grow. people also depend on coral reefs. the reefs contain many plants and animals used in medicines, chemicals, or other products we need to lead healthy lives.

4coral reefs grow best in clear, shallow water. here, the reefs can still get light from the sun to them grow. coral reefs grow about half an inch a year. they can grow much larger under perfect conditions. the great barrier reef off the coast of australia is the largest in the world. it is about 1,600 miles long and is made up of almost 3,000 individual reefs. it is so large that it can be seen from outer space. it is the world's biggest single structure made by living creatures.

5you might think coral reefs are very strong. they’re actually quite delicate. they can be harmed in many different ways. one way is when careless boaters drive in shallow waters. many divers hurt reefs by touching them. also hotel building near the reefs is very harmful, so is the waste that some people dump into the ocean.

6it’s very important for people to protect coral reefs. the reefs we have today started to grow thousands of years ago. it would take a long time for them to grow back if they were destroyed. scientists who study the reefs try to learn more and more about how they work. the information they learn will us keep the reefs safe for years to come.

the concluding sentence of this article

a) introduces a new question.
b) summarizes the entire article.
c) explains the meaning of a new word.
d) prepares readers for another paragraph.