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]: Couples spend ____ billion dollars a year on infertility treatments.
[A]: two


[Q]: Females usually reach sexual maturity at about four years of age, males at about ____ years.
[A]: six


[Q]: Black mustard contains ____ chemicals compounds, myrosin and sinigrin.
[A]:
two