What should the company do to guarantee the EC2 capacity?

Explanations:

Purchasing Reserved Instances guarantees a specific instance type in a particular Region but does not ensure capacity in the specified Availability Zones. Reservations can be spread across multiple Availability Zones but do not guarantee the availability of capacity in specific zones.

An On-Demand Capacity Reservation provides capacity in a specific Region but does not guarantee capacity in multiple Availability Zones unless specified. This option does not address the requirement for three specific Availability Zones.

While purchasing Reserved Instances can guarantee capacity in the specified Region, it does not ensure the capacity is available in the three specific Availability Zones needed for the event. It could lead to capacity being in only one or two zones, rather than all three.

Creating an On-Demand Capacity Reservation that specifies both the Region and the three specific Availability Zones ensures that the company has guaranteed capacity available for the required instances in those specific zones for the duration of the event. This is the most reliable method for guaranteeing EC2 capacity.