Read the following passage and mark the letter A, B, C or D to indicate the correct answer to each of the questions.

Coral reefs are the most diverse of all marine ecosystems. They are full of life, with perhaps one quarter of all ocean species depending on reefs for food and shelter. This is a remarkable statistic when you consider that reefs cover just a tiny fraction of the earth's surface and less than two per cent of the ocean bottom. Because they are so diverse, coral reefs are often called the rainforests of the ocean. Coral reefs are very important to people. They even provide seventy per cent of the food demands for some marine species, protection of shorelines, jobs based on tourism (nine out of twelve activities for tourists in Nha Trang, for example, involve the coral reefs), and even medicines.

Unfortunately, climate change is the greatest global threat to coral reef ecosystems. Scientific evidence now clearly indicates that the Earth's atmosphere and ocean are warming, and that these changes are primarily due to greenhouse gases derived from human activities.

As temperatures rise, mass coral bleaching events and infectious disease outbreaks are becoming more frequent. Additionally, carbon dioxide absorbed into the ocean from the atmosphere has already begun to reduce calcification rates in reef-building and reef-associated organisms by altering seawater chemistry through decreases in pH. This process is called ocean acidification.

Climate change will affect coral reef ecosystems, through sea level rise, changes to the frequency and intensity of tropical storms, and altered ocean circulation patterns. When combined, all of these impacts dramatically alter ecosystem function, as well as the goods and services coral reef ecosystems provide to people around the globe.

There are also many things you can do to ensure that you are environmentally conscious when you visit coral reefs or coastal areas. These include things such as hiring local guides to support the economy, removing all trash from an area, never touching or harassing wildlife in reef areas, and avoiding dropping your boat anchor or chain nearby a coral reef.

Finally, stay informed and spread the word! Educate yourself about why healthy coral reefs are valuable to the people, fish, plants, and animals that depend on them. Your excitement will help others get involved.

Though the coverage of coral reefs on the sea bed is ____, its vital role is undeniable.

• A. 
  remarkable
• B. 
  small
• C. 
  diverse
• D. 
  huge