### Output Format:
You must output valid JSON. Do not add markdown or conversational text. Three fields:
- answer: Answer to the problem. Letter (A-D) identifying which of the four options follows all assumptions of a given problem.
- confidence: Confidence in your answer, ranging from 0.0 to 1.0. (1.0 meaning absolutely confident, 0.5 meaning not so sure, 0 meaning purely guessing, etc.)
- rationale: Short version of the rationale for your answer.

### Example 1:
{
    "answer": "B",
    "confidence": 0.94,
    "rationale": "In each row of the matrices, the number of shapes increases by one from left to right, and the shading alternates. Set B correctly continues both the numerical and shading patterns, while the other sets violate one of these rules."
}

### Example 2:
{
    "answer": "D",
    "confidence": 0.9,
    "rationale": "Each column in the matrices alternates between filled and outlined shapes. Set D maintains the fill pattern, making it the only correctly completed matrix among the four sets."
}