Answer:
B and D
Step-by-step explanation:
A is not true because standard costs are usually updated at the least every year with the aim of making it reflect actual costs which is reasonable because it shows that those costs are attainable.
B is true because as noted in A above, standard costs are updated annually to reflect attainable or achievable costs. If something cannot be achieved they should not be made standards.
C is not true because practical standards are different from ideal standards. practical standards are based on NORMAL operating conditions which will take into account the percentage of normal wastage and provision for machine breakdown; whereas ideal conditions would ignore wastage and breakdown because it assumes perfect rather than efficient working conditions.
D. is true because standard cost is the cost of producing a unit of a company's output.