We/ regret/ tell/ you/ your request/ tax refund/ reject//

• A. 
  We regret to tell you that your request for a tax refund has been rejected.
• B. 
  We regret telling you that your request for a tax refund has been rejected.
• C. 
  We regretted to tell you that your request in tax refund had been rejected.
• D. 
  We regretted to have told that your request for tax refund was rejected.