In this task, find the most appropriate number to replace the blank (indicated with _ ) and express it in words.

[EX Q]: Every drug has _ names, a chemical name, a brand name, and an official name.
[EX A]: three

[EX Q]: Pups are unable to swim or find food until seven to _ weeks old or until the ice melts .
[EX A]: eight

[EX Q]: Man therefore has _ different substances interacting with each other.
[EX A]:
two