![](https://cos-cdn.shuashuati.com/pipixue-web/2020-1231-2005-12/ti_inject-812ce.png)
It is the level for which appropriate additional protective security measures shall be maintained for a period of time
A.
At this level, added protective security measures shall be kept all the times
B.
At this level, added protective security measures shall be kept for a period of time
C.
At this level, maximum protective security measures shall be kept for a period of time
D.
At this level, minimum protective security measures shall be kept all the times