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: Numbers can be positive or ____ only.

A: zero
****
Q: Fruit is a silique opening by ____ valves.

A: two
****
Q: Many animals use two or ____ forest structure types.

A:
three
****