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:
Birds have ____ basic types of feathers.
answer:
three


question:
Couples spend ____ billion dollars a year on infertility treatments.
answer:
two


question:
Acquired immunity is of ____ types, active and passive.
answer:

two