challenge: What is the main function of Stress-induced-phosphoprotein 1 (Hop)?
  
  A. To link Hsp70 and Hsp90 together
  B. To participate in the Hepatitis B virus reverse transcriptase complex
  C. To act as a receptor for prion proteins
  D. To modulate the chaperone activities of Hsp90 alone
  Answer: 