JT Engineering uses a two$-$step process to produce widgets. All widgets pass through the Smelting Department first and then through the Polishing Department. In terms of cost flow, which of the following describes the relationship of the Work in Process$-$Smelting and Work in Process$-$Polishing accounts to manufacturing costs?

They have no relationship to manufacturing costs; all manufacturing costs must be assigned to manufacturing overhead.

They have the same relationship to manufacturing costs; manufacturing costs can be assigned to either account.

They have a strictly sequential relationship to manufacturing costs; all manufacturing costs must be assigned to Polishing and then transferred to Smelting.

They have a strictly sequential relationship to manufacturing costs; all manufacturing costs must be assigned to Smelting and then transferred to Polishing.