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.

Q: Atoms are extremely small, on the order of a few ____ billionths of a meter.

A: ten
****
Q: Most spiders have eight eyes and ____ legs.

A: eight
****
Q: Mesons are combinations of ____ quarks .

A:
two
****