Before revision: In this paper, we conduct mathematical and numerical analyses  for COVID-19 . To predict the trend of COVID-19 , we propose a time-dependent SIR model that tracks  the transmission rate and the recovering rate at time t.
After revision: In this paper, we conduct mathematical and numerical analyses to address the following crucial questions for COVID-19 . To predict the trend of COVID-19 , we propose a time-dependent SIR model that tracks the transmission rate and the recovering rate at time t.