Correct

不备

/ bùbèi /
Strokes

Definition

unprepared/off guard

Example

As an Adjective

unprepared; off guard

1
chèn
bèi
le
xià
  

He struck me while I was off (my) guard.

2
bèi
不备

watch for a chance to take sb by surprise

3
Chéngbèi
乘其不备

catch sb off guard