Craft & Structure — module quiz

Text 1: Great tits nesting beside major roads sing at a higher minimum frequency than great tits in quiet woodland a few kilometres away — a difference of several hundred hertz, and one that holds across dozens of European cities. Because traffic noise is concentrated at low frequencies, researchers have taken the pattern as evidence that road noise is driving the difference. Text 2: Playback experiments make the mechanism concrete. The low notes of a great tit's song are exactly the ones traffic noise covers: recordings of low-pitched song played beside a road draw answering calls from rival males far less often than the same recordings played in woodland, while high-pitched song is answered at the same rate in both settings. Nor is the pitch fixed at hatching. Males that settled beside a newly opened motorway raised the minimum frequency of their songs within a single breeding season.

Based on the texts, which choice best describes the relationship between them?