TASK DEFINITION: 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.
PROBLEM: Copper has ____ naturally occurring isotopes.

SOLUTION: two

PROBLEM: Some rusts produce up to ____ different spore forms.

SOLUTION: five

PROBLEM: Ozone is a form of oxygen that occurs naturally, consisting of ____ oxygen atoms.

SOLUTION:
three