The question is simple, you have to find out who did it? However the way to the solution might be tricky and confusing. Just remember that only one of the statement is true and rest three are false.
1. Ms. Rihanna: 'Ms. Britney did it.'
2. Ms. Britney: 'Ms. Rihanna did it.'
3. Ms. Gwyneth: 'Ms. Britney’s telling the truth.'
4. Ms. Yoon: 'Ms. Gwyneth’s not lying.'