The correct answer is C. Consistency.
The written down value method of depreciation is a method of calculating depreciation that takes into account the fact that the value of an asset decreases over time. The value of an asset is reduced each year by a fixed percentage of its original value. This method is used because it is consistent and easy to understand. It is also a fair method of calculating depreciation, as it takes into account the fact that the value of an asset decreases over time.
The other options are not correct. Comparability is not a reason for using the written down value method of depreciation. Convenience is not a reason for using the written down value method of depreciation. None of these is a reason for using the written down value method of depreciation.