challenge: What does Shore's splitting theorem state about a recursively enumerable set A?
  
  A. A cannot be split into two recursively enumerable sets B0 and B1
  B. A can be split into two recursively enumerable sets B0 and B1, with A = B0 ∪ B1 and B0 ∩ B1 = ∅
  C. A can be split into two recursively enumerable sets B0 and B1, with A ≥α Bi for some i
  D. A can be split into two recursively enumerable sets B0 and B1, with A ≤α Bi for some i
  Answer: 