Final answer:
The phrase that best completes the sentence is 'una mochila' which means 'a backpack' in English.
Step-by-step explanation:
The phrase that best completes the sentence is OB. una mochila. This means 'a backpack' in English. Eduardo needs a backpack to store his books and other things. It is a common and practical item for students to carry their belongings.
Learn more about Completing a sentence in Spanish