Option A :- INCORRECT
No, the argument doesn't depend on the fact that cloth diapers are never disposed of, Although it is a known fact that it doesn't serve as an assumption on which the argument is built.
Option B :- INCORRECT
Well, doing things in the "old fashioned way" which is using cloth diapers isn't the reason nor the assumption to which the argument is built. The argument doesn't exist because there is a current trend in infant care that involves the use of cloth diapers.
Option C :- CORRECT
The process of using cloth diaper helps to reduce the use of natural resources used in making disposable diapers is the main cause of the argument, because the argument is concerned about how millions of trees can be saved each year if we use more of cloth diapers than disposable one that makes use of paper.
Option D :- INCORRECT
Quite true that modern people like convenience more than anything else, they may prefer disposable diaper than that of cloth diapers. This opposes the argument and doesn't serve as an assumption to which the argument is built.
Option E :- INCORRECT
The argument isn't concerned with the cost of any of the diapers, it is only concerned with the effect it has in nature.