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]: Deer mice have four toes on the forefeet and ____ toes on the hind feet.
[A]: five


[Q]: Bovine insulin differs from human in only ____ amino acid residues, and porcine insulin in one.
[A]:
three