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]: Tin exists in ____ allotropic forms.
[A]: three


[Q]: Conversations overlap, especially when more than three people try to talk in ____ room.
[A]: one


[Q]: Hybrid systems are dynamical systems with ____ levels of description.
[A]:
two