Magnetic fields

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 - Use of “which”
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 – changes the meaning.
E. 200,000 of that type existing worldwide and can interfere with pacemakers, and – changes the meaning.

B - Eliminate - "which" is redundant.
D & E - Changes the meaning.

Left with A & C

C - talks about the pacemakers hence also changes the meaning. But the sentence is about the magnetic fields.

Hence the answer is A.

A must be answer

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 - Correct

If we remove the bracketed portion, we still get a defined stem for the sentence: Researchers have announced that the magnetic fields emitted by one manufacturer’s security surveillance system can interfere with pacemakers and that this interaction can bring on missed or irregular heartbeats, nausea, breathlessness, dizziness, and even fainting. "that" usage makes the sentence parallel as well

B. of which, worldwide, there are 200,000 of that type, and which can interfere with pacemakers, and

No defined stem as the which before can interfere makes the portion a clause instead of a predicate that is required here.Other problem is the comma before 'and' is wrong - Option B is incorrect

C. (of which type there are 200,000 worldwide,) they can interfere with pacemakers and

Again if we omit the bracket out portion, the sentence stands as : Researchers have announced that the magnetic fields emitted by one manufacturer’s security surveillance system they can interfere with pacemakers and this interaction can bring on missed or irregular heartbeats, nausea, breathlessness, dizziness, and even fainting. - the they in the sentence breaks the flow. Option C is Incorrect

D. 200,000 of which type exist worldwide, interfering with pacemakers, and

Same problem as B's. interfering makes the required predicate a gerund . Inappropriate usage. D is incorrect. Other problem is the comma before 'and' is wrong

E. 200,000 of that type existing worldwide and can interfere with pacemakers, and
Other problem is the comma before 'and' is wrong
and breaks the normal flow of the sentence. Incorrect

Nothing seems to be wrong with A

Yes. A is the answer. But I found wrong answer in the set. It said D...but no way to be D.. should be A.

should be A.

Researchers have announced that X and that Y the bold portion is a give away.

A !

A

Another A