Alice is performing an experiment to determine which mouthwash kills the most bacteria. she is testing three different
mouthwashes. she uses four pieces of filter paper. each piece of filter paper was 3 cm in diameter. three of the pieces were
soaked in each mouthwash for 3 minutes each. the fourth piece was soaked in plain water for 3 minutes as well. each piece of
filter paper was placed on bacterial agar plate and covered. the agar plate was placed in a dark area and left alone for seven
days. after the seven days was up, alice measured the diameter of the bacterial rings around each piece of filter paper.
es -
the statement that best describes alice's experiment is

c. the experiment is well designed and have valid control