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

[EX Q]: Dairy cows live for _ generations, calve and produce normal milk on a protein-free diet.
[EX A]: six

[EX Q]: Sewage travels through _ different sets of pipes.
[EX A]: three

[EX Q]: Euthanasia rests on _ prongs.
[EX A]:
two