A. Add the w3-responsive class to a <div>.
B. Add the w3-container class to a <div>.
C. Add the w3-center class to a <div>.
D. Add the w3-block class to a <div>.

Solution

B. Add the w3-container class to a <div>.

Explanation

In W3.CSS, the w3-container class is used to provide proper padding and organize content in a responsive container.