Which contraceptive method does not offer STI protection?

Tubal ligation is a contraceptive method that involves surgically closing or blocking the fallopian tubes to prevent pregnancy. This method is highly effective at preventing conception, but it does not provide any protection against sexually transmitted infections (STIs). Unlike condoms, which create a barrier that can help prevent the exchange of bodily fluids and thus reduce the risk of STIs, tubal ligation is purely a means of birth control. It alters the reproductive system but does not affect the transmission of infections.

In contrast, condoms are designed specifically to reduce the risk of STIs while also preventing pregnancy. Similarly, the vaginal ring is a hormonal contraceptive method that primarily works to prevent ovulation but does not also act to block the transmission of infections like condoms do. Therefore, when considering STI protection, tubal ligation stands out as the method that does not offer any such protection, making it the correct answer.