D doesn't actually make any sense as an answer since it includes itself, i.e., we have that D={D,B}. Not only is this not allowed by the commonly used ZFC set theory due to the axiom of regularity, but if you were to try to compute D based on the rule, then you would end up with an infinite recursion that never terminates. Hence, determining the truth of D is an undecidable problem.
TL;DR; B is true, but it is impossible to say whether or not D is true.
All that is doing is including an answer that draws the attention away from the right answer, thereby being less specific to the question and less correct.
While that is logical is also incorrect in regards to test taking. With the answers given the one that creates the greatest exclusion from the others is "D". While "B" would be the reasonable choice, test taking strategy demands you select the answer which provides the most truths. "D" provides an additional truth and therefor the correct answer.