When referring to something that has no alternative, which article is used?

Key Points

Rule 8 states: "We also use the to refer to something that has no alternative. e.g. The sun is the source of energy in the earth."

Class 6 › English Grammar and Composition › Chapter 3: Articles: a, an, the › Topic: Use of a/an for first mention and unspecified items

Aligned to the NCTB national curriculum.