什么是 Barrier methods: the condom？

The condom — a thin sheath worn on the penis (a female version lines the vagina) — blocks the chain at the deposit step: the semen never enters the partner’s body. Widely available, needed only when needed — and unique on the shelf for a second service: it is the only method that also blocks the passage of the infections transmitted by sex, the subject of Chapter 69’s world. That double duty is why the condom stays in the picture even when another method is in use.