Revised Sentence:
The musty, unclean, and dark old room on the terrace was.
The sentence has been rearranged to correctly order the adjectives according to the rule of adjective order. Adjectives are typically placed in a specific order before a noun, which is: opinion, size, age, shape, color, origin, material, purpose. In this case, "musty" describes the opinion of the room, "unclean" describes the condition, and "dark" describes the color. Therefore, the revised sentence now follows the correct order.

Explanation:
- Adjective Order: Adjectives are used to describe or modify nouns. When multiple adjectives are used to describe a noun, they should be placed in a specific order for the sentence to make sense and sound natural.
- Original Sentence: The old room on the terrace was musty, unclean, and dark. This sentence did not follow the correct order of adjectives, which made it sound awkward and unclear.
- Revised Sentence: The musty, unclean, and dark old room on the terrace was. By rearranging the adjectives in the correct order, the sentence now flows smoothly and conveys a clear description of the room.
By following the rule of adjective order, the revised sentence provides a more accurate and coherent description of the old room on the terrace. It is important to pay attention to the order of adjectives in order to effectively communicate the intended description of a noun.