Final answer:
The best Spanish equivalent to 'Marcos opens his eyes quickly' is 'Marcos abre los ojos rápidamente'.
Step-by-step explanation:
The best Spanish equivalent to the phrase 'Marcos opens his eyes quickly' is Marcos abre los ojos rápidamente.
In Spanish, the adverb 'rápidamente' meaning 'quickly' modifies the verb 'abre' meaning 'opens'. The phrase 'Marcos abre los ojos' translates to 'Marcos opens his eyes', and 'rápidamente' adds the meaning of quickly to the sentence.
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