【名词&注释】
准备工作(preparation work)、专用工具(special tool)、气缸套(cylinder liner)、原动机(prime mover)
[单选题]_______means the level for which appropriate additional protective security measures shall be maintained for a period of time as a result of heightened risk of a security incident.
A. Security level 1
B. Security level 2
C. Security level 3
D. Security level 4