As far as we could see, the miles of copper-red grass were drenched in sunlight that was stronger and fiercer than at any other time of the day.

The sentence creates a vivid picture of a landscape: miles of copper-red grass are drenched in fierce sunlight. That appeals to the reader’s sense of sight, so the main device is imagery. “Copper-red” and “fiercer” are descriptive adjectives, but they help create the image rather than being the best answer to what the sentence as a whole uses.

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