Why can animals perceive these changes when humans can not ?

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Read the text carefully, then choose the most suitable answers.

A recent investigation by scientists at the US Geological Survey shows that strange animal behavior might help predict future earthquake.

Investigators found such occurrences in a ten-kilometer radius of the center of a fairly recent quake. Some birds screeched and flew about wildly. Dogs yelped and ran uncontrollably.

Scientists believe that animals can perceive these environmental changes as early as several days before the disaster.

In 1976 after observing animal behavior, the Chinese were able to predict a terrible quake. Although hundreds of thousands of people were killed, the government was able to evacuate millions of people and thus keep the death toll at a lower rate.