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: Carbon atoms are tetravalent, and therefore, can have ____ bonding pairs around each carbon atom.

A: four
****
Q: Most psychologists agree that the big ____ personality traits are stable across the life-span.

A: five
****
Q: Humans also walk upright on ____ legs.

A:
two
****