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]: Light chains exist in ____ classes, lambda and kappa.
[A]: two


[Q]: Some species take ____ to two years, or even more.
[A]: one


[Q]: Babies start swimming lessons as young as ____ weeks old.
[A]:
four