The answer is B
Alerts notify you when data in your dashboards changes beyond the limits you set. The limit can be above or below a threshold and can be set on cards, gauges and KPI visuals.
Answer D is incorrect. You do not write a custom R script for data alerts.
Answer C is incorrect. A subscription is a recurring snapshot of your dashboard sent to your email. A subscription is not used for data alerts.
Answer A is incorrect. You add emails for service notifications for admins in case of service disruptions.