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: Fish kills can occur when oxygen is less than ____ ppm.

A: three
****
Q: Respiratory therapists complete two to ____ years of education.

A: four
****
Q: Clinical depression lasts for at least ____ months.

A:
three
****