Read the passage.

Coral reefs are not just affected by human activity. Other organisms can do damage too. A nasty creature, the flatworm, is messing with the coral. The flatworm lives inside some species of coral. It affects its coral host by feeding on coral tissue and robbing the coral of nutrients it needs to survive.

Reread this sentence from the passage.

A nasty creature, the flatworm, is messing with the coral.

Which revision best expands the sentence to create a more formal style?

A) The flatworm is a parasite, and it’s a real problem for coral reefs these days.

B) A parasite that is threatening the health of coral reefs is the flatworm.

C) The flatworm makes life for coral miserable because it’s a parasite.

D) One major pain for coral reefs is the flatworm because it’s destructive.

B. A parasite that is threatening the health of coral reefs is the flatworm.

Explanation:

I used the process of elimination to see which statements were too casual.

In A., the phrase "it's a real problem" sounds like something someone could say to their friends when complaining about something, rather than an informative text.

C. says that it "makes life for coral miserable", which I was unsure of, but found the use of miserable to be interesting, since people rarely project emotions onto corals, of all animals. It's almost like personification, which is not a formal way of expressing an idea.

D. says "one major pain", which, like A., is something a friend could say to you when complaining.

Sorry, I know these explanations are sort of vague, since I go by ear, but it's how I would get the answer.

I hope this helps!

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explanation: