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

[EX Q]: All hairs have a life expectancy of _ to six years.
[EX A]: three

[EX Q]: Green energy comes in _ basic forms.
[EX A]: two

[EX Q]: Pinnipeds have four flippers - one pair in front, and _ pair in back.
[EX A]:
one