Which sentence uses commas correctly?


The tornado drill, I believe is held, so that we will know what to do in case of severe weather.


The tornado drill, I believe, is held so that we will know what to do, in case of severe weather.


The tornado drill, I believe is held so that we will know what to do in case of severe weather.


The tornado drill, I believe, is held so that we will know what to do in case of severe weather.