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

[EX Q]: Armaments manufacturers use lithium to produce tritium in _ ways.
[EX A]: two

[EX Q]: Ferrets bite in _ manners.
[EX A]: two

[EX Q]: Bulls reach the peak of their mating ability around the age of six to _ years.
[EX A]:
seven