Explanation:

- Nitrous oxide: It's a potent greenhouse gas. It traps heat in the atmosphere, contributing significantly to global warming.

- Water vapour: This is the most abundant greenhouse gas. It amplifies the greenhouse effect, as more water vapour can absorb more heat.

- Surface level ozone: This is a minor greenhouse gas. It contributes to warming but also harms human health and vegetation at ground level.

- Helium: It's an inert gas and not a greenhouse gas. It does not trap heat and has little interaction with the earth's atmosphere.

- Helium is the correct answer as it is not a greenhouse gas.

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