Select the most appropriate option to fill in the blank.
I don't like dirty cars, so you should keep it ______.

The sentence uses the conjunction "so" to show a logical result. If the speaker does not like "dirty" cars, the requirement is to keep the car perfectly clean. "Spotless" means absolutely clean or free from flaws/dirt, which serves as a direct context-based antonym to "dirty".
"Shabby" means in poor condition.

"Similar" means alike.

"New" refers to age, not cleanliness.