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

Q: Some school boards have _ teacher-librarians at all.

A: no
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Q: Giraffes have two horns and _ or three knobs.

A: two
****
Q: Caffeine has a purine ring in which each of _ nitrogen atoms bears a methyl group.

A:
three
****