Researchers have announced that the magnetic fields emitted by one manufacturer’s security surveillance system, of which type there are 200,000 worldwide, can interfere with pacemakers and that this interaction can bring on missed or irregular heartbeats, nausea, breathlessness, dizziness, and even fainting.
(A) of which type there are 200,000 worldwide, can interfere with pacemakers and that
(B) of which, worldwide, there are 200,000 of that type, and which can interfere with pacemakers, and
(C) of which type there are 200,000 worldwide, they can interfere with pacemakers and
(D) 200,000 of which type exist worldwide, interfering with pacemakers, and
(E) 200,000 of that type existing worldwide and can interfere with pacemakers, and
Spoiler

The correct answer is A. Choice A correctly utilizes parallel construction (Researchers have announced that...and that...); moreover, the "core" of answer choice A is grammatical (Researchers have announced that fields emited can interfere...and that this interaction can bring..)

Answer choice D, the supposedly correct response, contains several questionable elements. First, "200,000" of which type seems to actually question which type these security systems are. Second, magnetic fields "interfering" with pacemakers is an incorrect verb tense. Finally, choice D changes the intended meaning by implying that the machines rather than the magnetic fields are causing the problem.