i am confused between B and C.

Yep you are very right, thank you.

I didn't quite understand your question. Is it that you think "A" is better suited as the answer compared with "B"?

1st passage: Describes how coral reef community sustain in nutrient poor environment.
2nd passage: Describes how coral reef communities are threatened with increase in nutrition, caused by human activities, of water.

1st passage is giving us an information about coral reef communities that they flourish well in clear waters because of low nutrition level and 2nd is using the information to deduce that increase in nutrition of water, caused by human activities, is one of major causes of coral reef's deterioration.

Thus, the main intention of the author is to convey how human activities cause nutrition level change in the waters eventually affecting the reef community.

"B" is indeed the right choice.

"A":
Just one of statements in the passage mentions algae in it, conveying that abundance of algae in the waters is an indicator that coral reef is declining. This can't be the main concern of the author.
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~fluke

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I have few more questions on the same RC.

Folks please participate..


2. The passage suggests which of the following about coral reef communities?
(A) Coral reef communities may actually be more likely to thrive in waters that are relatively low in nutrients.
(B) The nutrients on which coral reef communities thrive are only found in shallow waters.
(C) Human population growth has led to changing ocean temperatures, which threatens coral reef communities.
(D) The growth of coral reef communities tends to destabilize underwater herbivore populations.
(E) Coral reef communities are more complex and diverse than most ecosystems located on dry land.


3. The author refers to “filter-feeding animals” (line 20) in order to
(A) provide an example of a characteristic sign of reef deterioration
(B) explain how reef communities acquire sustenance for survival
(C) identify a factor that helps herbivore populations thrive
(D) indicate a cause of decreasing nutrient input in waters that reefs inhabit
(E) identify members of coral reef communities that rely on coral reefs for nutrients

4. According to the passage, which of the following is a factor that is threatening the survival of coral reef communities?
(A) The waters they inhabit contain few nutrient resources.
(B) A decline in nutrient input is disrupting their symbiotic relationship with zooxanthellae.
(C) The degraded waters of their marine habitats have reduced their ability to carry out photosynthesis.
(D) They are too biologically complex to survive in habitats with minimal nutrient input.
(E) Waste by-products result in an increase in nutrient input to reef communities.

5. It can be inferred from the passage that the author describes coral reef communities as paradoxical most likely for which
of the following reasons?
(A) They are thriving even though human activities have depleted the nutrients in their environment.
(B) They are able to survive in spite of an over-abundance of algae inhabiting their waters.
(C) They are able to survive in an environment with limited food resources.
(D) Their metabolic wastes contribute to the degradation of the waters that they inhabit.
(E) They are declining even when the water surrounding them remains clear.

I don't have the OA

my answers

2 - A
3 - B
4 - E
5 - C

2. The passage suggests which of the following about coral reef communities?
(A) Coral reef communities may actually be more likely to thrive in waters that are relatively low in nutrients.
This is true. Keep this for now.
(B) The nutrients on which coral reef communities thrive are only found in shallow waters.
There is no proof within the passage that shows it ONLY thrives in shallow waters.
(C) Human population growth has led to changing ocean temperatures, which threatens coral reef communities.
The discussion of the threat is about increase in nutrient input not changing temperature. False.
(D) The growth of coral reef communities tends to destabilize underwater herbivore populations.
Destabilized herbivore pop. is a symptom of coral reef decline... D is twisted.
(E) Coral reef communities are more complex and diverse than most ecosystems located on dry land.
Coral reef has been contrasted with marine life not land animals.
ANSWER: A


3. The author refers to “filter-feeding animals” (line 20) in order to

Typical symptoms
of reef decline are destabilized herbivore populations and
(20) an increasing abundance of algae and filter-feeding animals

ANSWER: (A) provide an example of a characteristic sign of reef deterioration


4. According to the passage, which of the following is a factor that is threatening the survival of coral reef communities?

The passage says that its the increase in nutrient input... because of human activities... in second paragraph...
ANSWER: (E) Waste by-products result in an increase in nutrient input to reef communities.[b]

5. It can be inferred from the passage that the author describes coral reef communities as paradoxical most likely for which
of the following reasons?

(A) They are thriving even though human activities have depleted the nutrients in their environment.
[b]There is not example of this in the passage and no such discussion if humans deplete the nutrients in their environment. It is an extreme scenario not discussed in the passage.
(B) They are able to survive in spite of an over-abundance of algae inhabiting their waters.
False.
(C) They are able to survive in an environment with limited food resources.
BINGO! They survive in sparce food... as written in the last sentence of the first paragraph[b]
(D) Their metabolic wastes contribute to the degradation of the waters that they inhabit.
[b]They use metabolic wastes to survive... its the increase in nutrient input that is the problem.. two different things...
(E) They are declining even when the water surrounding them remains clear.
Not discussed in the passage