1. The children who attend that school receive a good education.
-> The children attending that school receive a good education.
2. Yuri Gagarin became the first man who flied into space.
-> Yuri Gagarin became the first man to fly into space.
3. The wild ox which is kept at Nam Cat Tien National Park is of a special kind.
-> The wild ox kept at Nam Cat Tien National Park is of a special kind.