Giraffes have anexcellent sense of vision and can see in color.  

The giraffes only produced the humming sounds at night when they couldn’t see one another.

Wild giraffes have never been recorded making humming sounds.  

Researchers observed other animals in European zoos humming.

English

PASSAGE: Scientists have long believed that giraffes are mostly silent and communicate only visually with one another. But biologist Angela Stöger and her team analyzed hundreds of hours of recordings of giraffes in three European zoos and found that giraffes make a very low-pitched humming sound. The researchers claim that the giraffes use these sounds to communicate when it’s not possible for them to signal one another visually.


 QUESTION: Which finding, if true, would most directly support Stöger and her team’s claim?