Which of the following is a key feature of responsive web design?

Flexible grids are a key feature of responsive web design because they allow the layout of a web page to adapt fluidly to different screen sizes and orientations. By using a grid system that employs relative units (such as percentages instead of fixed pixel values), the elements on the page can scale and reposition themselves in a way that optimally utilizes the available space on any device, whether it be a desktop, tablet, or smartphone. This adaptability is essential for providing an optimal viewing experience, ensuring that users have easy access to content regardless of the device they are using.

Other features such as fixed layouts, static images, or single platform support do not support the core principle of responsiveness, which is to create a flexible and adaptable web experience across various devices and screen sizes. Fixed layouts and static images can lead to a poor user experience on devices with different resolutions, while single platform support restricts accessibility and usability, which goes against the goal of responsive design.