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: Pathologists study four to ____ years after medical school and their postgraduate training.

A: five
****
Q: Scotch comes in ____ varieties, grain and malt .

A: two
****
Q: Natural silver contains ____ stable isotopes.

A:
two
****