Which of the following is true of a variable-interval schedule in operant conditioning?

The coronavirus disease 2019 is an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).[7] The disease was first identified in 2019 in Wuhan, the capital of China's Hubei province, and has since spread globally, resulting in the ongoing 2019–20 coronavirus pandemic.Common symptoms include fever, cough, and shortness of breath.Other symptoms may include muscle pain, sputum production, diarrhea, sore throat, loss of smell, and abdominal pain, PLEASE MARK BRAINLIEST..