To cry over ____ milk:

This question tests knowledge of common English idioms. Idioms are phrases where the meaning isn't obvious from the individual words.

• Correct Option B: "Split" is the correct word to complete the idiom "To cry over spilled milk." This idiom means to regret something that has already happened and cannot be changed. The past participle of 'spill' is 'spilled'.
• Option A: "Spoil" is incorrect. While milk can spoil, "spoil milk" is not part of this specific idiom.
• Option C: "Sour" is incorrect. Milk can turn sour, but "sour milk" is not used in this idiom.
• Option D: "Hard" is incorrect. Milk is not typically described as hard in this context, and it does not form part of the idiom.