There are hundreds of miles of undefended border between the two countries.两国之间有长达数百英里的不设防边境。We share the largest undefended border in the world.我们共享世界上最长的不设防边境。She scored a point when the goal was left undefended.她在球门没人防守的情况下进球得分。The fort was undefended and vulnerable.这个要塞没有设防，易受攻击。