Read the following passage and answer questions

A six year old boy was going through chemotherapy. He experienced severe nausea following each session. In between the sessions, his mother found that the boy experienced nausea after having his bath where he used the soap of brand 'X'. The mother found the smell of the soap similar to the medication used in the boy's chemotherapy. By the time his chemotherapy was over, the boy started showing symptoms of nausea to white attire, green wall paint, smell of any medicine and the sight of wheel chair. Once his treatment was over he had to visit the hospital every 15 days for his review check-up. In the first two review visits, he showed the symptoms of nausea which reduced by the time he went for his sixth review visit. By his sixth visit his nausea to the soap, white attire, green wall paint and wheel chairs disappeared.