Answer: wood because there is wood
The correct answer is Very young owls grow slowly.
Here, the adverb is <em>very </em>and the adjective is <em>young, </em>so the adverb is used to modify the adjective, or to show a particular degree of the adjective (how young? very young.).
In the rest of the options, there is only one adverb <em>slowly, </em>and it's not modifying an adjective, but rather the verb.
It can be considered as Greek mythology.
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