The correct options are
C An infinite or unspecified duration could result in voters not having a say in the matter when there is change desired.
D Being elected forever could result in representatives not remaining accountable to his/her voters.
If the candidates were to be elected and put in power forever, people could face the possibility of them abusing their power for their own gains. It could make them less accountable, decrease public participation and remove the element of choice for the average citizen given that elections would no longer be required for the candidate to stay in power.