//4a4. Select row document >
public string DocumentFind_MultiFilter(int year = 2004)
{
    // 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");


    //row dữ liệu sẽ lấy ra
    //var document = new BsonDocument
    //{
    //    { "student_id", 10000 },
    //    { "scores", new BsonArray
    //        {
    //        new BsonDocument{ {"type", "exam"}, {"score", 88.12334193287023 } },
    //        new BsonDocument{ {"type", "quiz"}, {"score", 74.92381029342834 } },
    //        new BsonDocument{ {"type", "homework"}, {"score", 89.97929384290324 } },                    
    //        }
    //    },
    //    { "class_id", 480}
    //};

    //select lấy row Document
    var highExamScoreFilter = Builders<BsonDocument>.Filter.ElemMatch<BsonValue>(
            "scores", new BsonDocument { { "type", "exam" },        // type là exam
            { "score", new BsonDocument { { "$gte", 80 } } }        // score có điểm > 80
        });


    var documentList = collection.Find(highExamScoreFilter).ToList();
    foreach (var row in documentList)
    {
        re += row;
    }

    return re;
}