reference,引用下列代码的运行结果？using System;namespace _08001{class Audi{ static void Main() {AAA a1 = new AAA();Do(a1);Console.WriteLine(a1.nA); } static void Do(AAA a2) {a2.nA = 7; }}class AAA{ public int nA; public AAA() {nA = 9; }}} 结果是好多？能不能给我一个详细的解释？