D. the squirrel's digestive system breaks down food for energy.
Because nowadays, many horses are domesticated, and food they would have eaten in the wild, they don't usually eat anymore. They have learnt to adapt to eating other foods, like hay, that require molars to ingest. This is why over time, their tooth structure has changed.
<span>B. They have continued to improve and are still used today.
The course of the Second World War gave rise to the technological advancements that are still being used today but now being improved.
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