Question
from Coral Reef Facts
This sentence is from the passage
Corals have a wide distribution in the world's oceans, but the
As coral thickets build upward on the skeletal remains of older
mi varteties that form reefs typically are restricted to relatively shallow, colonies, a reef is established." (Paragraph 2)
warm tropical waters between 30* north and south latitudes. Clean,
clear water with the right amount of nutrients is essential to their
What is the main role of this sentence in the passage?
I health. After initial colonization of a hard substrate and given
suitable conditions for coral growth, an individual larval "spatfall
• 1. to show that coral reefs are fragile
gives rise to a colony.
Given enough time, coral colonies become thickets. As coral
• 2. to show how coral reefs start to develop
thickets build upward on the skeletal remains of older colonies, a
reefs established. Today, richly diverse coral reefs are found along
3. to show that coral reefs constantly change
tropical coastlines, on the margins of volcanic islands, and as
isolated coral atons.
4. to show how coral reefs are like other coral forms
coral reers are dynamic, evolving through time into different
forms. Volcanic islands subside; that is, they have a tendency to
cool condense, and sink through time. As they subside, tropical
coral reefs grow upward along their margins.
Coral Reef Facts" by U.S. Geological Survey)
Answer
The main role of this sentence is to explain the process of how a reef is established through the growth of coral colonies.