instruction:
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.
question:
Copper has ____ naturally occurring isotopes.
answer:
two


question:
Variable stars fall into ____ major physical classifications.
answer:
four


question:
Ordinary tin is composed of ____ stable isotopes.
answer:

nine