15. The non-transitory machine-readable medium of claim 10 , wherein the operations further comprise: determining whether there is a prior query that the user has not responded; and transmitting the prior query to the user device to request the user to respond, in response to determining that there is a prior query that the user has not responded.
15. The non-transitory machine-readable medium of claim 10 , wherein the operations further comprise: determining whether there is a prior query that the user has not responded; and transmitting the prior query to the user device to request the user to respond, in response to determining that there is a prior query that the user has not responded. 16. The non-transitory machine-readable medium of claim 15 , wherein the operations further comprise: tracking how many times the prior query has been sent to the user device; and marking the prior query to prevent the prior query from being sent to the user device again, in response to determining that the prior query has been sent to the user device for more than a predetermined number of times.