Final answer:
To conjugate the verb 'abrir' in the sentence 'Marcos (abrir) el libro a la página 5,' we add the correct ending 'e,' resulting in 'Marcos abre el libro a la página 5.'
Step-by-step explanation:
The subject of this question is Spanish. The question asks to conjugate the verb 'abrir' in the sentence 'Marcos (abrir) el libro a la página 5.' To conjugate the verb 'abrir' in the present tense for the third person singular subject 'Marcos,' we add the correct ending 'e,' resulting in 'Marcos abre el libro a la página 5.'
Learn more about Conjugating the Spanish verb 'abrir' in the present tense