Which key usually follows the tonic key in a major-key sonata-form exposition?

In a major-key sonata-form exposition, the key that usually follows the tonic key is the dominant key.12

The exposition is characterized by tonal contrast, where the music begins in the home key and moves to a closely related but distinct key. For a work in a major key, the dominant—the key whose keynote is five tones above the tonic—is the standard choice for this second tonal area.1