List＜对象＞某成员 集合 转字符串，用逗号隔开

List<test> list = new List<test>();
var a = from o in list select o.成员A.ToString();
var b = from o in list select o.成员B.ToString();
string s1 = string.Join(",", a.ToArray());
string s2 = string.Join(",", b.ToArray());