Many seemed to regard this as an expression for almost any undesirable (agent) in buildings: electric and magnetic fields, asbestos, toxic chemicals in building materials etc. What does the word in brackets mean in this sentence?
A.a person who works for a country’s secret service B.a person who looks after someone else’s business affairs C.a person who gets work for an actor or musician D.a chemical or a substance that produces an effect or a change正确答案D
