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

[EX Q]: Immune response improves in about _ weeks.
[EX A]: four

[EX Q]: Men produce brand new sperm every _ to three months.
[EX A]: two

[EX Q]: Hexapods comprise insects and three small orders of insect-like animals with _ thoracic legs.
[EX A]:
six