Nathan, a new Agile practitioner, is at a planning event where the relative development effort of user stories of a large product backlog is to be estimated. The planning event is mostly conducted in silence and the team is to assign user stories to various T $-$ shirt sizes $($ small $,$ ?medium, large, extra $-$ large $).$ ?The planning event is efficient and the user stories are estimated quickly. What type of planning event is Nathan most likely attending?

Infinity estimating

T $-$ shirt estimating

Affinity estimating

Relative estimating