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]: Fruit is a silique opening by ____ valves.
[A]: two


[Q]: Eternity is a game for one to ____ players, human or computer.
[A]:
four