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.

Seismologists offer ____ major theories for the occurrence of large, deep earthquakes.
three

Female smokers enter menopause an average of ____ years earlier than nonsmokers.
five

Humanity is responsible for ____ or six billion tons a year.

five