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

[Q]: Metals often crystallize in a _ dimensional version of the hexagonal closest packed structure.
[A]: three


[Q]: Gerbils get reproductive when they reach sexual maturity at the age of _ months.
[A]: three


[Q]: Many eye disorders have _ symptoms until it is too late.
[A]:
no