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

[EX Q]: Prolactin exists in _ heterogenic forms which possess varying biological activity.
[EX A]: three

[EX Q]: World population continues to rise, even as a few countries move toward _ growth.
[EX A]: zero

[EX Q]: Osteoporosis is _ times more common in women than men.
[EX A]:
eight