GMAT Verbal Practice, Reading Comprehension
The levels of dissolved oxygen in the world’s ocean waters are declining precipitously. Just like humans, fish need oxygen to survive, and so in ocean areas experiencing significant levels of oxygen scarcity, or hypoxia, fish populations are plummeting. Although some hypoxic areas, called “dead zones,” occur naturally, hypoxia in coastal areas and inland waters is caused mainly by agricultural run-off and by discharge of industrial waste waters. More than one-hundred permanent dead zones, many covering thousands of square miles, exist worldwide today.
Since reproductive success is the most critical factor in the sustainability of any species, the extent of this threat to marine life and genetic diversity can hardly be overstated. After several months in hypoxic waters, female fish produce fewer eggs. Moreover, hypoxic conditions serve to alter the normal ratio between two particular hormones manufactured during the embryonic stage when a fish’s gender is determined. During gestation and under these conditions, the mother produces more testosterone (and less estradiol), which inhibits the development of female reproductive organs and other female characteristics in the embryo, while promoting the development of male traits.
Which of the following is the best title for the passage?
- Why are Fish Gender Ratios Changing so Rapidly?
- Dead Zones: Their Causes and Consequences
- The Dangers of Industrial Waste-water Runoff
- A Prescription for Reversing Hypoxia Levels
- What Causes Birth Defects in Salt-water Fish?
The first paragraph briefly discusses what causes hypoxic waters (so-called "dead zones"), while the second paragraph discusses one of hypoxia's consequences: a decline in the genetic diversity and population of fish. Choice (B) is the only one that embraces the entire passage without extending beyond its ideas. The correct response is (B).