如何将字符串转换为小写字符串？

var str = "Hello World";
var lowerStr = str.toLowerCase();
console.log(lowerStr); // 输出：hello world

str = "Hello World"
lower_str = str.lower()
print(lower_str) # 输出：hello world

String str = "Hello World";
String lowerStr = str.toLowerCase();
System.out.println(lowerStr); // 输出：hello world

string str = "Hello World";
string lowerStr = str.ToLower();
Console.WriteLine(lowerStr); // 输出：hello world