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]: Snowmobiles can accommodate ____ riders per vehicle.
[A]: two


[Q]: Fish kills can occur when oxygen is less than ____ ppm.
[A]: three


[Q]: Evolution is dependent on ____ forces.
[A]:
two