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If an object hadn’t crashed into Earth to form the moon, as is hypothesised, Earth would be bigger. Would it still sustain life?

Chris Arnott,

Hitchin, Hertfordshire, UK

Given the number of cars on the roads now, what are the chances of my remote key fob unlocking another car (and vice versa)?

Chris Humphries,

Keadby, Lincolnshire, UK

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