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.

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

[EX Q]: Collages can have two or ____ layers.
[EX A]: three

[EX Q]: Plants obtain food in ____ different ways.
[EX A]:
two