Alexander Fleming Had Been Running Tests Using Staphylococcus, and He

Alexander Fleming had been running tests using Staphylococcus, and he left some plates out to incubate. Evidently, after returning to his lab after the weekend, he found that Penicillium mold was growing on his agar plates containing the growth of Staphylococcus. Looking more closely, he
Found a large, clear area around the mold colony where Staphylococcus colonies did not grow. Given this situation, a valid hypothesis would be that ________.

A) the Staphylococcus was being inhibited by the Penicillium mold
B) the Penicillium mold was being killed by the Staphylococcus
C) the bacteriological medium being used in the plates was somehow inhibitory to the Staphylococcus growth
D) the room temperature incubation was inhibitory to the growth of Staphylococcus