challenge: Which of the following proteins is NOT an inhibitor of apoptosis protein containing the inhibitor of apoptosis domain (BIR)?
  
  A. BIRC2 (cIAP1)
  B. BIRC1 (NAIP)
  C. BIRC7 (apoptosisinhibitor)
  D. BIRC4 (xIAP)
  Answer: 