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Fill in the blanks to complete the student's slightly panicked email to the professor.
Sarah and _________________________ tried to finish the final project on time, but the computer suddenly crashed on _________________________ right before the midnight deadline.
Sarah and I tried to finish the final project on time, but the computer suddenly crashed on us right before the midnight deadline.
I is a subject pronoun. It is part of the compound subject "Sarah and I" performing the action of trying. (Tip: Try removing "Sarah and"—you would say "I tried", not "me tried").
Us is an object pronoun that follows the preposition "on".