sentence2_structure: Environmental changes<>is<>most responsible for the extinction of most species of plants and animals$$$plants and animals<>have lived<>on earth
sentence1: Most extinctions are thought to have resulted from environmental changes that affected the species in either of two ways.
sentence2: Environmental changes is most responsible for the extinction of most species of plants and animals that have lived on earth.
question: What process is most responsible for the extinction of most species of plants and animals that have lived on Earth?