Yes, I also saw such arguments in J.Hull chapters. In fact, these two choices were confusing! I'm not confident that I have marked the answer in respect to Libor quotation in major currencies. But more likely, I think I have marked the final one.
Regarding the proxy advantage of overnight swap index over Libor, recently some investors and analytics considered or argued it to be as proxy especially during the recent crisis. So, as a whole OIS is not recognized to be as proxy. As a consequence, LIBOR is widely used proxy for valuation and pricing.
really confusing answers.....