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: Some of the plant and animal species that once live here adapted to changes, others are extinct.
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?