Sentence:  The FBI typically does not investigate adult <WSD>prostitution</WSD>, leaving it as a state and local matter, but in recent years it has made child <WSD>prostitution</WSD> a priority in a program the FBI calls Operation Cross Country. The program includes highway billboards asking people to call the FBI with tips. 
Meaning of the word marked with <WSD> tags:  Engaging in sexual activity with another person for pay.