What does a Quick Response (QR) code primarily consist of?

A Quick Response (QR) code primarily consists of black squares. These codes are designed to be scanned by smartphones and other devices that can read the patterns encoded within the graphic. The black squares are arranged in a specific manner, forming a matrix that encodes information such as URLs, text, or other data.

The use of black squares is essential for the QR code's functionality because it allows the scanner to differentiate between the areas of the code that represent data and the areas that do not. The contrast between the black squares and the white background aids in quick recognition and scanning, which is a key feature of QR codes.

In this context, while other options might mention shapes or patterns, none capture the specific design and purpose of QR codes as accurately as the presence of black squares does.