Task: Question Answering
Input (English): Background Paragraph: Retinitis is inflammation of the retina in the eye, which can permanently damage the retina and lead to blindness. The retina is the part of your eye that is also known as the "sensing tissue." Retinitis may be caused by a number of different infectious agents. Retinitis, also called Retinitis pigmentosa, has a prevalence of one in every 2,500-7,000 people. This condition is one of the leading causes that leads to blindness in patients in the age range of 20–60 years old. 
Story: John is comparing his medical record with his father's and son's medical records. John is 40 years old; his father is 70 years old; and his son is 10 years old. It appears that both John and his father has Retinitis. But his son does not have Retinitis. 
Question: Who is most probably infected by infectious agents, John or John's son?
Output (English): John.