a. not perceived or discerned
a. 未被发现的
1. The virus remained undetected for several months.
这个病毒在几个月内未被发现。
2. Some problems can go undetected until they become serious.
一些问题可能会在变得严重之前未被发现。
3. The thief escaped undetected through the back door.
小偷通过后门逃走了，未被发现。