Final answer:
The correct verb to fill in the blank is 'hace'.
Step-by-step explanation:
The correct verb to fill in the blank in the sentence is hace. The sentence 'tres años que hablo español' translates to 'it has been three years since I speak Spanish.' The verb 'hace' is used to indicate the passage of time and in this case, it expresses the duration of how long the speaker has been speaking Spanish.
Learn more about Spanish verbs