The answer is A: a flagship species.
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NAD+ accepts a hydrogen ion (H+) and two electrons (2e−), as it becomes reduced to NADH + H+. The NADH moves to the electron transport chain and donates a pair of electrons (becomes oxidized) to the first compound in the chain.
Explanation:
1. A
2. E
3. C
4. B
5. F
6. G
7. D