(D) is incorrect because the argument is not a circular argument. Identify the conclusion and the premises. The conclusion here is that the videos are extremely effective, but the videos' effectiveness is not cited as evidence for this conclusion, which is what would be required for (D) to be correct.
(B) is explained in another thread on this question, but essentially, (B) is too extreme of an assumption. There is no mention of the effectiveness being "always directly proportional" to the number of times a direction is repeated. Keep a lookout for extreme words such as "always" on the LSAT. Also, in this case, a DIRECT proportion has no evidence for it either. Hope this helps!