使用注释来描述以下变量的正确数据类型：
var length = 16; // @(6)
var lastName = "Johnson"; // @(6)
var x = {
firstName: "John",
lastName: "Doe"
}; // @(6)
var length = 16; // Number
var lastName = "Johnson"; // String
var x = {
firstName: "John",
lastName: "Doe"
}; // Object
var length = 16; // NUMBER
var lastName = "Johnson"; // STRING
var x = {
firstName: "John",
lastName: "Doe"
}; // OBJECT
var length = 16; // number
var lastName = "Johnson"; // string
var x = {
firstName: "John",
lastName: "Doe"
}; // object