instruction:
In this task, find the most appropriate number to replace the blank (indicated with _ ) and express it in words.
question:
Friction occurs when _ objects rub together.
answer:
two

question:
Pets also track in pollen, and _ out of every ten people is allergic to cat or dog dander.
answer:
one

question:
Fitnesses are important numbers in evolutionary theory and can be estimated by _ main methods.
answer:
three