Answer:
Option A, To minimize recall bias of exposure
Step-by-step explanation:
In a case control study, two group as are studied and compared on the basis of some supposed causal attribute
In this case the supposed causal attribute is association of down syndrome in children with the occupational radiation exposure of their fathers.
If the parents are interviewed about their history of occupational radiation exposure, there are high chances of them making mistakes while recalling.
Hence, instead of interview paternal radiation exposure was taken from employment records
Hence, option A is correct