Câu hỏi:

Read the following passage and mark the letter A, B, C, or II to indicate the answer to each of the question.

As Hurricane Florence zeroes in on the southeastern US, scientists are warning that climate change is exacerbating the effect of tropical storms. The powerful Category 4 Atlantic weather-front is slow moving, an increasingly common phenomenon that poses a different manner of threat to states in its path. In the event that Florence stalls or comes to a halt altogether over land, it has the potential to deposit catastrophic quantities of rainwater, posing a risk of severe flash flooding.

While the high winds and waves generated by faster storms moving inland from the ocean pose a significant danger to human life and property, the effect of heavy rain can be just as devastating, if not more so. When Hurricane Harvey hit in August 2017, it dropped 60 inches of rain over Houston, Texas, flooding the streets, leaving 93 dead and hundreds more having to be rescued by boat, causing millions of dollars-worth of damage.

James Kossin of the National Oceanic and Atmospheric Administration published a study in the journal Nature in June suggesting that slow-moving tropical cyclones, which would include those like Florence and Harvey, have become more common over the last 70 years, dropping in speed by 10 per cent in that time. According to Mr Kossin, global warming as a result of man-made air pollution is causing the poles to become warmer, which in turn reduces the difference in temperature between the Arctic and Antarctic and the equator, altering atmospheric pressure and slowing down the whipping currents of wind that pass between them and drive hurricanes.

The word “which” in paragraph 3 refers to ______.