With reference to Conceptual Framework of IFRS, and to the relevant standards $($IAS or IFRS$),$ answer the questions about the following cases. Your answer should evaluate the case and make a comment whether the case or the company's practice is correct, and your answer should include a reference to the appropriate standard.

a$)$ In $2022,$ Brown Company used lower of cost and net realizable value principle of IAS $2$ in valuing its inventories and calculated a write$-$down amount of $4,350$ OMR. The company recorded the amount into an account under shareholders' equity.

b$)$ As per the regulations, Brown Company is required to publish its financial statements according to IFRS. Brown company has been using First$-$in$,$ First$-$out as the cost flow method in its inventories for several years. In $2023,$ the company decided to use Last$-$in$,$ First$-$out cost flow method.

c$)$ Blue&Green Company adopts IAS $16$ in accounting for its property, plant and equipment. In $2023,$ the company decided to use cost model for the subsequent measurement of its administrative buildings but decided to use revaluation model for factory buildings.

d$)$ DarkBlue Company is considering choosing a depreciation method for its machines. The accounting team suggested a depreciation method that is based on revenue that is generated by an activity that includes the use of the machines, because they believe that this method will better represent the changes in the value. IAS $16$