What is the difference between a barrier reef and an atoll?
a. barrier reefs surround an active volcano emerging above sea level, while atolls surround the previous location of a submerged volcano.
b. atolls surround an active volcano emerging above sea level, while barrier reefs surround the previous location of a submerged volcano.
c. atolls surround an inactive volcano emerging above sea level, while barrier reefs surround the previous location of a submerged volcano.
d. barrier reefs surround an inactive volcano emerging above sea level, while atolls surround the previous location of a submerged volcano.

c. Atolls surround an inactive volcano emerging above sea level, while barrier reefs surround the previous location of a submerged volcano.

Explanation:

A barrier reef will grow in the surroundings of an island, it is the shelter for different species, fish, and plants. If the environmental conditions are good, the reef will tend to grow during certain time. With the movement of the tectonic plates, the island can sink trough the time, and new corla reef can grow.

Now is an atoll that can have an inactive volcano and could have some coral rings around,

So the main difference is the presence of a soil body, surrounded by reef.  

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humans have been a key factor in climate change around the globe since the start of the industrial revolution, and in the past few decades the consequences are becoming more obvious. there's lots of emission of pollutants in the atmosphere as well as changing the environment on the surface itself, so it's really hard to predict how will that go in the future because there's some countries that are reducing the damage and are going towards green energy, while others are stubbornly continuing with pollution and damages to the environment.