The w3-border-0 class in w3.css removes all borders from an element. When this class is applied, it eliminates any borders around the element entirely.

Explanation of the other options:

• (A) "It has rounded borders": This is incorrect because w3-border-0 removes borders, it does not round them.
• (C) "removes rounded borders only": This is also incorrect because w3-border-0 removes all borders, whether they are rounded or not.
• (D) "None of these": Since (B) is correct, this option is not the right choice.