C#.NET正则表达式问题

string pattern = @"a\d+";
string input = "apple123 banana456 cherry789";
MatchCollection matches = Regex.Matches(input, pattern);
foreach (Match match in matches)
{
    Console.WriteLine(match.Value);
}

string input = "Please send your queries to support@example.com. Also, you can reach others at contact@example.org and info@example.net";
string pattern = @"\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b";
MatchCollection matches = Regex.Matches(input, pattern);
foreach (Match match in matches)
{
    Console.WriteLine(match.Value);
}

string input = "Hello world! This is a test.";
string pattern = @"\b\w+\b";
string replacement = "****";
string result = Regex.Replace(input, pattern, replacement);
Console.WriteLine(result);

string pattern = @"^\d{3}-\d{3}-\d{4}$";
MatchCollection matches = Regex.Matches("123-456-7890", pattern);
foreach (Match match in matches)
{
    Console.WriteLine("Valid phone number");
}

string pattern = @"^\d{4}[-]?\d{1,2}[-]?\d{1,2}$";
MatchCollection matches = Regex.Matches("2022-01-01", pattern);
foreach (Match match in matches)
{
    Console.WriteLine("Valid date");
}