Step 1: Understand the usage of adjectives.
The word "beautiful" is an adjective used to describe a noun. Here, it describes the "day."
Step 2: Analyze each option.
- (A) beauty: This is a noun, not an adjective.
- (B) beautify: This is a verb, and it doesn’t fit in the context.
- (C) beautiful: Correct. "Beautiful" is the appropriate adjective to describe the day.
- (D) beautification: This is a noun, and doesn’t fit grammatically in the sentence.
Step 3: Conclusion.
The correct adjective to describe the day is "beautiful."