The correct answer is: A. summarize flow of output.
A process costing system is a type of accounting system that is used to track the costs of production in a manufacturing environment. The first step in a process costing system is to summarize the flow of output. This means identifying the different stages of production and tracking the units that are transferred from one stage to the next. Once the flow of output has been summarized, the next step is to compute output in units. This involves determining the number of units that have been completed and the number of units that are still in process. The final step in a process costing system is to summarize total costs. This involves identifying the different types of costs that are incurred in the production process and tracking the total amount of each type of cost.
Option B is incorrect because the first step in a process costing system is to summarize the flow of output, not compute output in units.
Option C is incorrect because the first step in a process costing system is to summarize the flow of output, not summarize total costs.
Option D is incorrect because the first step in a process costing system is to summarize the flow of output, not compute cost for each equivalent unit.