You can create a budget in Azure cost management and also create an action group to notify when costs are being breached.

Option A is partially correct but is only viable before creating resources in Azure.
Option C is incorrect since this is ideal when you want to have recommendations in place in Azure.
Option D is incorrect since this is ideal from a billing perspective and segregation on costs.
https://docs.microsoft.com/en-us/azure/cost-management/tutorial-acm-create-budgets