are being produced,have been produced.has been produced:as if,ev

are being produced,have been produced.has been produced:as if,even if，as for
How often do we hear someone say,“I walked into the room,and something just doesn't seem right."It may be that the person is sensing chemical messages that ______ by others-______ those individuals are no longer present.
【正确答案】：have been produced; even if