Answer:
Come is to go as to is to leave.
The appropriate answer for the blank in the given sentence is 'leave'.
This is because 'come' and 'go' are two opposites that are commonly used to describe the act of entering or leaving a place, and 'to' and 'leave' are also opposites used in the same context.
Therefore, the two pairs of words, 'come' and 'go' and 'to' and 'leave', have the same relationship.