下面哪个JSON格式表示(姓名John，年龄30，来自城市New York)是有效的？（ ）
{ "name": "John", "age": 30, "city": "New York" }
{ "name";"John","age";"thirty","city";"New York" }
{ "name": John, "age": 30, "city": "New York" }
{ name: "John", age: 30, city: "New York" }