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.

Sexual maturity is reached within ____ to four years.
two

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

Antibiotic prophylaxis is warranted only in patients with ____ or more exacerbations per year.
four