Concept:The expression "building castles in the air" is an idiom meaning daydreaming or making plans that have no real chance of succeeding.Explanation:"Castles in the air" are not real buildings; they exist only in imagination.So, a person who builds castles in the air creates ideas or goals that are not grounded in reality.Such goals are usually impossible to achieve or lack a solid foundation.Therefore, Joe is someone whose aims cannot be realistically accomplished.Answer:B. has goals that are impossible to achieve.