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

[EX Q]: Healthy people can donate blood as often as once every _ weeks.
[EX A]: eight

[EX Q]: Ticks are small round arachnids with _ legs and can have either a soft or hard body.
[EX A]: eight

[EX Q]: Fertilizer is applied according to soil tests taken every three to _ years.
[EX A]:
four