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.

Counterpoint is simply ____ or more melodies played simultaneously.
two

Hedgehogs give birth to one to ____ babies which are born with the spines just below the skin.
seven

Radiologists train three to ____ years to improve their perception.

four