instruction:
In this task, find the most appropriate number to replace the blank (indicated with _ ) and express it in words.
question:
Ozone is a form of oxygen in which the molecule contains _ atoms instead of two.
answer:
three


question:
Gravity is the weakest of all _ forces but unlike the others it has an unlimited range.
answer:
four


question:
Ozone leaves _ by-products except pure oxygen.
answer:

no