What is the C# equivalent of the Oracle PL/SQL COALESCE function?

//pseudo-codeish
string s = Coalesce(string1, string2, string3);

object obj = Coalesce(obj1, obj2, obj3, ...objx);

object obj = Coalesce(obj1, obj2, obj3, ...objx);

object obj = obj1 ?? obj2 ?? obj3 ?? ... objx;

var a = b ?? c;

var a = b != null ? b : c;