Final answer:
The correct answer is A. estuve, the past tense of the verb 'estar' (to be), which translates to 'I was' in English.
Step-by-step explanation:
The subject of this question is Spanish, as the sentence is written in Spanish, and the options are related to Spanish grammar and vocabulary.
The correct answer is A. estuve. This is the past tense of the verb 'estar' (to be) in the first person singular. It translates to 'I was' in English, which fits the sentence: 'Yesterday I was sick all day.'
Keywords: Spanish, past tense, estar, sick, all day
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