IMO C
Strengthen means proicide support to premise or assumption to reach the concl :
A->physical fitness service being often offered does not strengthen that they are helpful to employee and employer !!!No comments about increased productivity and reduced absenteesm etc!!Just saying this service is a big hit or often used does not explain why its good Eliminate
C is just better in the given scenario !!!it just strengthens the premise that physical health of emloyees is improved by regular exercise !!!But yes no where in the argument regular exercise is mentioned !!But among given FIVE optins this is the best.
Answer: C