Complex sentence: The song is in the key of F. The melody appears to fluctuate from this home key, however, through its avoidance of perfect cadences, as the dominant, C7 chord resists anchoring on the tonic I chord of F major.
Split into simpler sentences: The song is in the key of F, yet the melody appears to fluctuate from the home key. This results from the avoidance of perfect cadences, as the dominant, C7 chord resists anchoring on the tonic I chord of F major.