//4d1. UpdateOne row document
public string DeleteMany()
{
    // Replace the uri string with your MongoDB deployment's connection string.
    var client = new MongoClient(
        "mongodb://localhost:27017/?readPreference=primary&appname=MongoDB%20Compass&directConnection=true&ssl=false"
    );

    string re = "";

    //lấy database
    var database = client.GetDatabase("HvDadabase");
    //Lấy List Collection
    var collection = database.GetCollection<BsonDocument>("HvCars");

    //select lấy 1 row Document            
    var deleteLowExamFilter = Builders<BsonDocument>.Filter.ElemMatch<BsonValue>("scores",
            new BsonDocument { { "type", "exam" }, {"score", new BsonDocument { { "$lt", 60 }}}
    });

    re = "dữ liệu trước khi delete : <br/> ";
    var documentList = collection.Find(deleteLowExamFilter).FirstOrDefault();
    foreach (var row in documentList)
    {
        re += row + "<br/>";
    }


    //Update 1 row tìm thấy dầu tiên
    collection.DeleteMany(deleteLowExamFilter);


    re += "<br/> dữ liệu sau khi update : <br/> ";
    documentList = collection.Find(deleteLowExamFilter).FirstOrDefault();

    foreach (var row in documentList)
    {
        re += row + "<br/>";
    }

    return re;
}