Context: The passage below describes an experiment.

Cameron and his friend Elizabeth flew nylon kites on the beach. They wondered if putting a tail on a kite would affect how well the kite flew.
Cameron flew a kite that did not have a tail for five minutes. Then, he attached a four-foot-long tail and flew the kite for five more minutes. Cameron repeated this with three similar kites, alternating whether he started the kite with or without a tail. During each flight, Elizabeth counted the number of times the kite crashed to the ground.
Figure: flying a kite.
In this experiment, which were part of an experimental group?
A. the kites with tails
B. the kites without tails
From the given choices, select the correct answer and reply with the letter of the chosen option.

A