If it is an essay the conclusion should contain a short summary of what the key pointes
1. A source of oxygen
2. Something to control temperature; we humans need a temperature that is neither too hot nor too cold.
3. Protection from sunlight
4. Water
5. Food
If the underlined part of the sentence us <em>used today, </em>then the correct answer is D. adjective phrase.
It isn't a clause because there is no verb here, so it is an adjective phrase.
