The word “it” in paragraph 4 refers to . - Học để khẳng định mình

The word “it” in paragraph 4 refers to .

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions.

The Gulf of Mexico could see one of its largest dead zones on record this summer, according to researchers. A "dead zone" is known in scientific literature as hypoxia, which means low oxygen. This water, with its low concentration of dissolved oxygen, can no longer support the life that calls that part of the ocean home. Dead zones were first noticed in the area in the 1970s, and they've been growing in size ever since. Based on current conditions, some scientists think that the Gulf of Mexico will witness the second-largest dead zone on record in July.

Louisiana State University (LSU) scientists predict that 8,717 square miles of bad water will be at the bottom of the continental shelf off Louisiana and Texas, making it about the same size as the state of New Jersey. "We think this will be the second-largest, but it could very well go over that," said Nancy Rabalais, a marine ecologist who has been studying this phenomenon for over 34 years and who is co-author of the LSU report. The National Oceanic and Atmospheric Administration (NOAA), using a different model to make its calculation, also released a dead zone prediction report and anticipates a slightly smaller dead zone of 7,829 square miles. However, that's still larger than the average measured size of the dead zone.

The dead zone is connected to runoff from one of the largest rivers in the world, the Mississippi. What happens, Rabalais explains, is that too many dissolved molecules of nitrogen and phosphorus from runoff stimulate the growth of phytoplankton, which fall to the bottom and decompose. This degradation uses up oxygen in the water, which leads to the creation of dead zones.

The Gulf's dead zone is considered the world's largest, but it isn't the only area with a dead zone. There's one in the Chesapeake Bay and another in the Baltic Sea. There are about 500 coastal areas that have these dead zones at some part of the year. With climate change bringing more rain, there will be more record dead zones in the future, Rabalais thinks.

Not much can be done to stop the formation of this enormous dead zone from happening this year, but there is something that can be done to prevent problems in the future. The US Environmental Protection Agency has a task force looking at the issue, as do several states. Farmers themselves have also actively taken action by creating embankments that reduce erosion and retain runoff. "These are actions that are better for the environment, and they're still profitable, sometimes even more profitable”, said Rabalais. More, though, needs to be done. "I'm an optimist by nature, but that optimism does not cover the weather. This is a long-term trend that is likely to stay around," she said. "I hope I will be around long enough to see this change."
(Adapted from

ID [755990]

The word “it” in paragraph 4 refers to __________.

A. the world’s largest
B. dead zone
C. area
D. the Gulf
Đáp án. D

Lại Thị Lan

Dẫn chứng: The Gulf's dead zone is considered the world's largest, but it isn't the only area with a dead zone. (Vùng chết của vùng vịnh được coi là lớn nhất thế giới, nhưng đây không phải là khu vực duy nhất có vùng chết.)