A researcher wanted to determine the effect water temperature has on goldfish respirations. The researcher placed the goldfish in three different bowls of water with three different temperatures and counted the goldfish's respirations for two minutes in each setting.
What factors must be kept constant to obtain valid results ?
O length of time, size of tank, volume of water
O water temperature, length of time, volume of water
number of respirations, volume of water, the goldfish
the goldfish, size of tank, water temperature