Final answer:
The correct word to fill in the blank in the given sentence is 'que'.
Step-by-step explanation:
In the given sentence, the correct word to fill in the blank is que. Hace tres horas, Olivia espera que el autobús llegue. The word que is used to introduce a subordinate clause that expresses purpose or intention. In this case, Olivia is waiting for the bus to arrive.
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