วิธีประกาศ array แบบไม่กำหนดขนาด ใน C# ทำอย่างไรครับ

string[] s = new string[] { };

using System.Collections;

	string[] arr1 = new string[] { "one", "two", "three" };
	string[] arr2 = { "one", "two", "three" };
	var arr3 = new string[] { "one", "two", "three" };

	string[] arr4 = new string[3];
	arr4[0] = "one";
	arr4[1] = "two";
	arr4[2] = "three";