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.

Example Input: Millipedes have ____ pairs of legs on each body segment.
Example Output: two

Example Input: Most organ systems are operational in the fetus by ____ to six months.
Example Output: four

Example Input: Attainment designation refers to the levels of ____ criteria pollutants in the air.
Example Output:
six