<qa>  What is the combination pill that will be used in this study?No single strategy for the prevention of HIV has emerged as consistently used and successful, so multiple strategies have been developed. PrEP involves delivering ARV medications to people before they are exposed to HIV, in order to prevent infection. The optimal method of delivering PrEP has not yet been determined. This study will examine the feasibility of delivering PrEP in three methods. Daily dosing involves receiving ARV medications every day; time-driven dosing involves receiving ARV medications twice weekly plus a post-exposure dose; and event-driven dosing involves receiving ARV medications before and after a potential exposure to HIV. The ARV medication that will be used in this study is a combination pill that contains emtricitabine and tenofovir disoproxil fumarate FTCTDF. Recent research studies have shown that, if taken consistently, a daily oral dose of FTCTDF can reduce the risk of HIV infection. 