Final answer:
The source document used to assign direct labor to each particular job is a time ticket, which tracks employee hours spent on specific jobs for accurate billing and labor cost assessments.
Step-by-step explanation:
The source document used to assign direct labor to each particular job is known as a time ticket. Companies use time tickets to track the number of hours that employees spend on specific jobs. This allows for accurate billing of labor to the correct job and assists in labor cost analysis. The direct association between the labor costs and the job makes the job costing process more precise. A job cost sheet, on the other hand, compiles all costs related to a particular job, but it is not the source document for assigning labor specifically. Similarly, a requisition form is generally used for materials requests, and a subsidiary ledger is an extension of the general ledger used for organizing and summarizing specific types of transactions. Therefore, the correct answer is: a. time ticket.