OG-34-216

Passage 34

Coral reefs are one of the most fragile, biologically

complex, and diverse marine ecosystem on Earth. This

ecosystem is one of the fascinating paradoxes of the bio-

sphere: how do clear, and thus nutrient-poor, waters sup-

(5) port such prolific and productive communities? Part of the

answer lies within the tissues of the corals themselves.

Symbiotic cells of algae known as zooxanthellae carry out

photosynthesis using the metabolic wastes of the coral

thereby producing food for themselves, for their corals,

(10) hosts, and even for other members of the reef community.

This symbiotic process allows organisms in the reef com-

munity to use sparse nutrient resources efficiently.

Unfortunately for coral reefs, however, a variety of

human activities are causing worldwide degradation of

(15) shallow marine habitats by adding nutrients to the (water.

Agriculture, slash-and-burn land clearing, sewage disposal

and manufacturing that creates waste by-products all

increase nutrient loads in these waters. Typical symptoms

of reef decline are destabilized herbivore populations and

(20)an increasing abundance of algae and filter-feeding

animals.

Declines in reef communities are consistent with observa-

tions that nutrient input is increasing in direct proportion to

growing human populations, thereby threatening reef com-

(25) munities sensitive to subtle changes in nutrient input to

their waters.

216. 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.

OG 解释C 没有提到。可是

Symbiotic cells of algae known as zooxanthellae carry out

photosynthesis using the metabolic wastes of the coral

thereby producing food for themselves, for their corals,

(10) hosts, and even for other members of the reef community.

This symbiotic process allows organisms in the reef com-

munity to use sparse nutrient resources efficiently.

可不可以推出光合作用在清水里更有效率？

我不认为应该有此推论。文中并没有将不同环境中的光和作用效率进行比较。我们也不用多想。否则思维更混乱。

thanks. i found it also, there is much more clear indication in the text.