Which of the following describes a ‘basic standard’ within the context of budgeting?

A. A standard which is kept unchanged over a period of time
B. A standard which is based on current price levels
C. A standard set at an ideal level, which makes no allowance for normal losses, waste and machine downtime
D. A standard which assumes an efficient level of operation, but which includes allowances for factors such as normal loss, waste and machine downtime