instruction:
In this task, find the most appropriate number to replace the blank (indicated with _ ) and express it in words.
question:
Natural iron contains _ isotopes and isomers.
answer:
four

question:
Some bird feeders have _ perches at all, but neither do tree trunks.
answer:
no

question:
Most sharks have _ different kinds of fins, which lift, stabilze and propel the shark.
answer:
five