Premise: Skeptic used video tape to remove the possibility of sleight of hand, supplies standard deck to remove the possibility of trick deck and selected card by himself/herself to remove possibility of planted volunteer.
Conclusion: The skeptic concluded that Debbie uses neither sleight of hard, nor a trick deck, nor a planted "volunteer" to achieve her effect
(A) The skeptic failed to consider the possibility that Debbie did not always use the same method to achieve her effect.
Yes correct, if each time cheat technique changed between 3 techniques then we can't conclude that based on these trials that all 3 techniques have not been used.
(B) The skeptic failed to consider the possibility that sleight of hand could also be detected by some means other than videotaping.
It could have been detected by other method, but still it could have been caught using video tap also. We have not given videotape was effective or not. Hence eliminate.
(C) The skeptic failed to consider the possibility that Debbie requires both sleight of hand and a trick deck to achieve her effect.
It both are required than magician must have caught in 2 of the things. But magician came out clear, this means all 3 mentioned technique have not been used. Instead of criticizing it is supporting.
(D) The skeptic failed to consider the possibility that Debbie used something other than sleight of hand, a trick deck, or a planted "volunteer" to achieve her effect.
Author is concerned about that magician didn't use mentioned 3 tricks, he/she didn't bother weather some other technique have been used. Eliminate.
(E) The skeptic failed to consider the possibility that Debbie's success in the three trials was something other than a coincidence.
This is similar to D, Even if it is other than coincidence like some possibility outside of 3 discussed in passage didn't affect our conclusion that mentioned 3 tricks have not been used.