Choose the correct option to fill in the blank.
______ sun is not the biggest star but it is the nearest star to us.

Correct option is A

The correct option to fill in the blank is (a) The.
Explanation:
The Sun is a unique celestial body in our solar system. We use the definite article the before names of unique objects because there is only one such object in the given context.
The correct sentence is:
The sun is not the biggest star but it is the nearest star to us.
Example:
· The Moon revolves around the Earth.
· The Sun rises in the east.
Why other options are incorrect:
· (b) No article needed: Incorrect because unique objects take the.
· (c) A: Incorrect because there is only one Sun in our solar system.
· (d) An: Incorrect because sun begins with a consonant sound and refers to a unique object.
Information Booster:
Use the before unique objects:
· the Sun
· the Moon
· the Earth
· the Universe
· the Equator
· the North Pole
Exception:
When referring to other stars as suns in astronomy, sun may be used as a common noun.
Example:
Scientists have discovered a planet orbiting a sun similar to ours.