Correct answer: (b) 1, 2 and 4 only
Explanation
- A
1, 2, 3 and 5 only
1, 2, 3 and 5 only. Microwave ovens and phone lines are not the keyed magnetite sources.
- B
1, 2 and 4 only
1, 2 and 4 only. Brake wear, engines and power plants throw magnetite nanoparticles. Microwaves and telephone lines are out.
- C
3, 4 and 5 only
3, 4 and 5 only. Wrong trio.
- D
1, 2, 3, 4 and 5
All five. 3 and 5 fail.
Summary. Official key is (b) 1, 2 and 4 only. Airborne magnetite linked to brain studies comes from vehicle brakes and engines and from coal-fired plants. Home microwaves and telephone lines are not that source list.
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