A 40 yrs old man underwent kidney transplantation for end stage renal disease.Two months after transplantation,he developed fever and features suggestive of bilateral diffuse interstitial pneumonia.Which one of the following is the most likely etiological agent?

• A. Herpes simplex virus
• B. Cytomegalovirus
• C. Epstein-Barr virus
• D. Varicella-zoster virus