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

Q: Humans host _ species of louse, the head louse , the body louse and the pubic louse .

A: three
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Q: Psychiatrists say one out of _ people are mentally ill.

A: four
****
Q: Tamarins have _ to three babies a year.

A:
one
****