The sentence to be corrected is embedded within the quotes,

"That every worker has a clean criminal record is of some importance to investment banks which is why a stringent background check is a necessary prerequisite for all of their job applicants."

a- That every worker has a clean criminal record is of some importance to investment banks which is why a stringent background check is a necessary prerequisite for all of their job applicants
b- Clean criminal records of their employees is important to investment banks; hence, a stringent background check are necessary prerequisites for employment
c- Because they consider it important that all of their employees have a clean criminal record, investment banks require each job applicant to undergo a stringent background check
d- It is of some importance that all investment banks’ workers have clean criminal records which is why many of them undergo stringent background checks
e-The reason that investment banks require background checks of their applicants is because they require clean criminal records of their employees