Which of these gives the statement of one-dimensional steady-state diffusion problem?

• A. The diffusive flux of Φ leaving the exit face is the same as the diffusive flux of Φ entering the inlet face
• B. The diffusive flux of Φ leaving the exit face plus the diffusive flux of Φ entering the inlet face is equal to the generation of Φ
• C. The diffusive flux of Φ leaving the exit face minus the diffusive flux of Φ entering the inlet face is equal to the generation of Φ
• D. The diffusive flux of Φ leaving the exit face is the same in magnitude and opposite in direction as the diffusive flux of Φ entering the inlet face