As the efficiency of the catalytic converter drops through the deterioration, the switching rate of the rear O2 sensor signal will start to look like the front O2 sensor signal. When the rear O2 sensor signal reaches approximately 75% of the front O2 sensor, which of the following is the result?

A. The diagnostic trouble code is stored with the MIL on.
B. A one trip flag is set with the code stored, but the MIL isn't activated.
C. The catalytic converter should be replaced.
D. The catalyst beads in the converter should be changed.

If you have no clue, please don't answer.