Answer :
a . Nonsteroidal antiinflammatory drugs (NSAIDs). NSAIDs are likely causing Walden Macnair's abdominal pain due to their known gastrointestinal side effects.
Walden Macnair, a 35-year-old male, was admitted to the hospital for the first time with symptoms of abdominal pain. The pain started about 3 hours ago, is described as burning, and is related to eating. His condition is stable, and his history reveals that he has been taking medications for knee problems over the last three months.
Given these details, the most likely type of medication responsible for causing his symptoms is nonsteroidal anti-inflammatory drugs (NSAIDs). NSAIDs can irritate the stomach lining, leading to symptoms such as burning abdominal pain related to eating.