event/christies_24477/1 matches the site

public static Activity Auction_Event()
{
    var auction = new Activity()
        .WithContext()
        .WithId("https://linked.art/example/event/christies_24477/1")
        .WithLabel("Impressionist Sale")
        .WithClassifiedAs(Aat.AuctionEvent);

    auction.IdentifiedBy = [new Name("Impressionist & Modern Evening Sale").AsPrimaryName()];

    auction.TimeSpan = new LinkedArtTimeSpan
    {
        Label = "Nov 5, 2014",
        BeginOfTheBegin = new LinkedArtDate(2014, 11, 5, 17, 0, 0),
        EndOfTheEnd = new LinkedArtDate(2014, 11, 5).EndOfDay()
    };

    auction.TookPlaceAt = [
        new Place()
            .WithId("https://linked.art/example/place/christies_nyc")
            .WithLabel("Christie's, New York")
            .WithClassifiedAs(Aat.Term("300005234", "Auction House (place)"))
    ];

    auction.CarriedOutBy = [
        new Group()
            .WithId("https://linked.art/example/group/christies")
            .WithLabel("Christie's")
            .WithClassifiedAs(Aat.Term("300417515", "Auction House (organization)"))
    ];

    return auction;
}

• Role shortcuts AsPrimaryName, AsAccessionNumber and AsSystemAssignedNumber each add a single classification, with the AAT terms Primary Name, Accession Number and System Number.
• Terms outside the registry The vocabulary registry holds only the terms linked.art itself publishes, so a dataset's own concepts, places and people are written with Aat.Term, Tgn.Place and Ulan.Person, giving the id and the label.

var activity = new Activity
{
    Context = ["https://linked.art/ns/v1/linked-art.json"],
    Id = "https://linked.art/example/event/christies_24477/1",
    Label = "Impressionist Sale",
    ClassifiedAs = [Aat.AuctionEvent],
    CarriedOutBy =
    [
        new Group
        {
            Id = "https://linked.art/example/group/christies",
            Label = "Christie's",
            ClassifiedAs = [Aat.Term("300417515", "Auction House (organization)")],
        },
    ],
    IdentifiedBy =
    [
        new Name("Impressionist & Modern Evening Sale")
        {
            ClassifiedAs = [Aat.PrimaryName],
        },
    ],
    TimeSpan = new LinkedArtTimeSpan
    {
        Label = "Nov 5, 2014",
        BeginOfTheBegin = new LinkedArtDate(2014, 11, 5, 17, 0, 0),
        EndOfTheEnd = new LinkedArtDate(2014, 11, 5, 23, 59, 59),
    },
    TookPlaceAt =
    [
        new Place
        {
            Id = "https://linked.art/example/place/christies_nyc",
            Label = "Christie's, New York",
            ClassifiedAs = [Aat.Term("300005234", "Auction House (place)")],
        },
    ],
};

Generated from the object the example builds: every property that is set, as object initialisers, with the vocabulary constants where a term is in the registry. The fluent helpers are a convenience, not a requirement; this form and the one as written produce the same JSON.