In this task, find the most appropriate number to replace the blank (indicated with _ ) and express it in words.

[Q]: Willow flycatchers have a lifespan of _ to four years.
[A]: three


[Q]: All imaginary numbers are complex numbers with _ for the real part.
[A]: zero


[Q]: Lightning can travel _ miles or more horizontally from the storm, then strike the ground.
[A]:
six