밑줄 친 부분 왜 for which 인가요?
그냥 which 만 쓰면 안되는 건가요? 시험범위라 자세히 설명 좀 부탁드립니다.

unfortunately, the patent expired in the meantime. the same goes for the computer mouse, the patent for which expired in 1980, just before the concept became popular, and the rollerblade skates, the patent for which expired in 1985, just before the rollerblade craze started.