Concept:The phrase "gone around the bend" is an idiomatic expression meaning to become crazy or mentally unstable.Explanation:"Gone around the bend" is informal English.It suggests losing one's mental balance or ability to reason properly.In the sentence, the speaker is sad because his friend has become mentally confused, not because the friend travelled, lost a job, or fell ill.This makes "gone mad" the most appropriate interpretation among the options given.Answer:B. gone mad