Concept:An error of principle happens when a transaction is entered in the wrong type of account, such as mixing up capital expenditure and revenue expenditure.
Explanation:Motor Vehicle Account is an asset, so buying or maintaining a vehicle is capital expenditure.
Motor Expenses Account is an expense, so it is revenue expenditure.
Debiting the Motor Vehicle Account instead of Motor Expenses Account mixes these two different classes of accounts.
This mistake does not affect the trial balance because both accounts are debited and credited correctly in amount.
Therefore, it is classified as an error of principle.
Answer:D. principle