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]: Marine biologists have ____ theories on why whales breach.
[A]: two


[Q]: Spermatogenesis creates ____ sperm of equal size.
[A]: four


[Q]: Stems are of ____ types, flowering and vegetative.
[A]:
two