challenge: What is the primary use of martinostat when tagged with the radioisotope carbon-11?
  
  A. To study the effects of HDAC inhibition on recombinant class I HDACs
  B. To quantify HDAC in the brain and peripheral organs using positron emission tomography
  C. To selectively target class I HDACs in tissue assays
  D. To inhibit class IIb HDACs in peripheral organs
  Answer: 