Final answer:
The indicator that revenue for a service can be recognized over time is the seller enhancing an asset that the buyer controls as the service is performed. Estimating the percent of work completed is necessary for measuring progress, but by itself does not indicate revenue can be recognized over time. A fixed sales price is required for revenue recognition but does not determine the timing of revenue recognition.
Step-by-step explanation:
The indicator that revenue for a service can be recognized over time is A) The seller is enhancing an asset that the buyer controls as the service is performed. According to accounting standards, this suggests that the control over the services provided is being transferred progressively, and thus, revenue can be recognized as work is completed. This is different from recognizing revenue at a single point in time, which normally occurs when a service is distinct and the control is transferred upon completion of that service.
In the context of revenue recognition, the provision of continuous effort to the buyer may also be a factor considered by some accounting frameworks. However, it is not as definitive as when the seller is enhancing an asset that the buyer controls.
The ability to estimate the percent of work completed is part of the process for measuring progress toward completion, which is necessary for revenue recognition over time, but the mere ability to estimate does not, by itself, determine whether revenue can be recognized over time.
A fixed and determinable sales price (D) is required for revenue recognition in general, but it is not an indicator of whether revenue can be recognized over time or at a single point in time.