Context: The passage below describes an experiment.

Stefan was a chef's assistant in an Italian restaurant. One of his coworkers told him that adding salt to water would cause the spaghetti to cook faster.
Stefan gathered six pots that were the same size. He filled each pot with the same amount of pure water. He added one tablespoon of salt to each of three pots. He did not add salt to the other three pots. Then, Stefan boiled spaghetti in each pot. He checked how firm the spaghetti was after five minutes of boiling.
Figure: spaghetti in a pot.
In this experiment, which were part of an experimental group?
A. the pots with salted water
B. the pots with pure water
Choose the right answer from the options and respond with its letter.

A