Use the following information when answering the following question In 1668, Francesco Redi performed a series of experiments on spontaneous generation. He began by putting similar pieces of meat into eight identical jars. Four jars were left open to the air, and four were sealed. He then did the same experiment with one variation: Instead of sealing four of the jars completely, he covered them with gauze (the gauze excluded the flies while allowing the meat to be exposed to air). In both experiments, he monitored the jars and recorded whether or not maggots (young flies) appeared in the meat. What hypothesis was being tested in the initial experiment with open versus sealed jars? a. Maggots do not arise spontaneously, but from eggs laid by adult flies. b. The type of meat used affects the likelihood of spontaneous generation c. Spontaneous generation is more likely during the long days of summer. d. Spontaneous generation can occur only if meat is exposed to air

The meat in the open jars can be directly accessed by the adult flies for consumption. While accessing the food, some of these adult flies can lay egg into the jars which hatch to give rise to new maggots.
The meat in jars closed by a gauze is exposed to the air but cannot be accessed by the adult flies as the flies are prevented from entering into the jar due to the presence of the gauze. As a result of this the flies do not consume meat, nor do they lay eggs and so no maggots will appear in this jar.