{
    "_id" : ObjectId("5a2bb526398b444facaba1c0"),
    "ProductId" : 1,
    "Combination" : {
        "Manufacturer" : "xxx",
        "Model" : "yyy",
        "Color" : "blue",
        "Thickness" : "9 mm"
    },
    "CreatedOn" : ISODate("2017-12-09T10:04:22.654Z"),
    "CreatedBy" : 0,
    "ModifiedOn" : Date(-62135596800000),
    "ModifiedBy" : 0,
    "ExcelId" : 10
}

/* 2 */
{
    "_id" : ObjectId("5a2bb526398b444facaba1c1"),
    "ProductId" : 1,
    "Combination" : {
        "Manufacturer" : "xxx",
        "Model" : "bbbb",
        "Color" : "green",
        "Thickness" : "9 mm"
    },
    "CreatedOn" : ISODate("2017-12-09T10:04:22.654Z"),
    "CreatedBy" : 0,
    "ModifiedOn" : Date(-62135596800000),
    "ModifiedBy" : 0,
    "ExcelId" : 10
}

var combCol = db.GetCollection("zAttributeCombinations").AsQueryable<zAttributeCombinations>();

                var variables = (from c in combCol
                                 where c.ProductId == ProductId **(&& Manufacturer = "xxx" && Model = "yyy" && Color="blue")**
                                 select new
                                 {
                                     Combination = c.Combination
                                 }).ToList();