a. lacking necessary documents (as for e.g. permission to live or work in a country)
a. 无正式文件的, 无事实证明的
1. Many undocumented immigrants live in fear of being discovered.
许多无证移民生活在被发现的恐惧中。
2. The school provides support for undocumented students to help them succeed.
学校为无证学生提供支持，帮助他们取得成功。
3. Undocumented workers often take low-paying jobs because they have limited options.
无证工人通常从事低薪工作，因为他们的选择有限。