The correct answer is: A. response time
Response time is the elapsed time between the instant at which a user requests some information and the instant at which the information is delivered or becomes available for use. It is a measure of how quickly a system responds to a request.
Waiting time is the time spent waiting for a response. It is the time between the instant at which a request is made and the instant at which the request is accepted for processing.
Processing time is the time spent processing a request. It is the time between the instant at which a request is accepted for processing and the instant at which the response is generated.
Turnaround time is the total time between the instant at which a request is made and the instant at which the response is received. It is the sum of waiting time, processing time, and transmission time.
In the context of the question, the elapsed time between initiating a query and receiving a response is called response time.