Given a sentence, fill out the missing word with a 'no' or a number (between zero and ten). You should write the numbers with english alphabet, like: four instead of 4.
--------
Question: Sponges are subdivided into ____ classes.

Answer: three


Question: Stereo cameras track the fly's movement in ____ dimensions.

Answer: three


Question: Most men sleep for eight hours when ____ are sufficient.

Answer:
seven