Step 1: Read the sentence carefully and note the comparison being made.
“What could make for \underline{\hspace{2cm}} Diwali than that?”
Step 2: The word than indicates a comparison between two situations.
Step 3: For short adjectives like happy, the comparative degree is formed by changing -y to -ier.
Happy $\rightarrow$ happier
Step 4: Option (C) is incorrect because it uses a double comparative (more happier).
Option (D) is incorrect because the superlative form is not required.
Step 5: Therefore, the correct sentence is:
“What could make for a happier Diwali than that?”