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

[EX Q]: Water is the only substance on earth that exists naturally in _ states .
[EX A]: three

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

[EX Q]: Teeth begin to come in, or erupt, around age _ months.
[EX A]:
six