PART A: The statement that best expresses a theme of the short story "Examination Day" is C. High intelligence can be viewed as a dangerous thing.
PART B: The detail from the text that best supports this answer is D. "'We regret to inform you that his intelligence quotient is above the Government regulation, according to Rule 84 Section 5 of the New Code.'" (Paragraph 56).
This quote highlights that high intelligence is not only seen as undesirable by the government but is also regulated, suggesting that it can be deemed dangerous or problematic.