Yes this is a hard one. I don't have an answer as well. But if I was forced to choose I'd probably choose (D), for the following reason:
A. Although it fills all of the classes it opens, Fitness Express’s share of all health club memberships has declined over the last five years.
That's why the plan to advertise more and open more classes will work.
B. Fitness Express’ number of classes offered to their clients has declined slightly over the last year.
Again that's why they should open more classes.
C. Advertising has made the name of Fitness Express widely known, but few customers know that Fitness Express health clubs also off acupuncture and shiatsu treatments.
That's why it should advertise more about these unknown classes.
D. Fitness Express’s health clubs is one of three clubs that have together accounted for 88% of health club memberships.
If they already have very large of market share they may have already got all the members that they could get. There might not be many people that can be attracted to them who are not yet one of their members.
E. Despite a slight decline in membership price, sales of Fitness Express memberships have fallen in the last five year.
That's why they need to do more advertising and adopt other means to attract customers, such as open more classes.