First of all, PLEASE don't post the answer. You could have taken the snapshot, without selecting the correct answer.
IMO D ->
A/E - "....length of which is that of...." is an awkward construction.
Also, in A "..., and it weighs..." antecedent of "it" is not clear. "It" is refering to camcorder or computer..
In B/C, "...world, which...." Here "which" is refering to the world instead of refering to camcorder
In D, "...digital camcorder, which...." is correct construction and D has no pronoun reference error