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]: Natural ytterbium is a mixture of ____ stable isotopes, with seven other unstable isotopes known.
[A]: seven


[Q]: Stems are of ____ types, flowering and vegetative.
[A]: two


[Q]: Cankers develop slowly and can take ____ months to girdle a stem.
[A]:
four