<qa>  What is the double barrier method for female subjects?Female subjects of child-bearing potential must agree to use two forms of highly effective contraception from the last menstrual period prior to randomization or use a double barrier method as described below until they are on two forms of highly effective contraception for at least one menstrual cycle, during the study treatment, and for 3 months after the final dose of study treatment. Female subjects exempt from this requirement are subjects who practice total abstinence. If currently abstinent, the subject must agree to use a double barrier method of contraception, i.e., condom and occlusive cap diaphragm or cervicalvault caps with spermicide or until they are on two forms of highly effective contraception for at least one menstrual cycle if they become sexually active during the study treatment and for 3 months after the final dose of study treatment. Highly effective contraception includes: 