Let A be a square matrix whose entries are integers. Which of the following is true?
 a)    If detA = ± 1 then 
 need not exist
  b)   If detA = ± 1 then 
 exists but all its entries are not necessarily integers.
  c)    If detA ≠ ± 1 then 
 exists and its entries are non-integers.
  d)   If detA = ± 1 then 
 exists and its entries are integers