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

[EX Q]: Planaria has rudimentary eyes which produce _ images but detect direction.
[EX A]: no

[EX Q]: Bacteria acquire genes conferring resistance in any of _ ways.
[EX A]: three

[EX Q]: Infected pigs can shed the virus in their faeces for up to three to _ weeks after infection.
[EX A]:
four