PTC.S3.Q18 MBF Chelas and Stelma

Vectorthesupercutecat

Can anyone please help explain this question? very confused..
My thought:
C and S are required to leave their respective stations immediately to pursue any prisoner who attempts to escape.
prisoner escape --> leave
unless they are pursuing such a prisoner, C and S are forbidden to leave until their replacements have arrived.
leave --> replacement arrived or pursue prisoner ??? is that correct?
On 9-11pm, when they finished shifts and replacement arrived, it was discovered that C had violated these rules and S has not.
Pick could be true except:
A prisoner attempted to escape at 7pm, neither C or S left his or her station before 9pm.
Why is this the correct answer?
All the answer choices don't really make any sense to me. Not sure how to apply because the one person violate the other one did not situation completely threw me off...
Please help! Thank you!!!!