请教个试题

You have a UTIL_IMPACT_LIM of 50 and a UTIL_IMPACT_PRIORITY of 60 for the backup utility What
are the maximum amount of system resources that the backup utility can use?
A. 30%
B. 40%
C. 50%
D. 60%

搞不懂答案为什么是A呢，不应该是C. 50%吗？搞不懂，请大侠们指导。