A. The most recent National Conference of Mathematics Teachers addressed the problem of convincing students who
=> Nothing wrong with it yet, let's keep.
B.
The most recent problem faced by the National Conference of Mathematics Teachers was
convincing students who
=> Changing the meaning of the original sentence => eliminate, also pretty sure the use of "V-ing" here is wrong
C. The most recent National Conference of Mathematics Teachers addressed the problem of convincing students
whom=> Wrong use of "whom" => eliminate
D.
Most recently, the National Conference of Mathematics Teachers addressed the problem of convincing students who
=> Changing the meaning of the original sentence => eliminate
E. The most recent National Conference of Mathematics Teachers
addressed those students who=> Changing the meaning of the original sentence => eliminate