87.
A:
current problems I might arise in the future I it is unlikely I practice existed
B:
commonplace problems I rarely occurred I it would be difficult to contend I was an everyday occurrence
C:
problems of the future I were widespread I one should not rule out the possibility I was a deep-rooted practice
D:
existing problems I might arise in the future I it would not be unreasonable to argue I was a widespread practice
The answer is: D