BD+C:
Option 1, under naturally ventilated spaces, change B to D
Option 2, 2,under naturally ventilated spaces, change B to D and C to E.

ID+C:
Option 1, under naturally ventilated spaces, change B to D
Option 2, under naturally ventilated spaces, change B to D and C to E; under mixed-mode systems, change C to D and D to E.