Welcome to the Lounge

string[] strings = 
{
    "A penny saved is a penny earned.",
    "The early bird catches the worm.",
    "The pen is mightier than the sword." 
};

string vowels = "aeiou";

List<string> vowelstartwords = String.Join(" ", strings)
        .Split(' ')
        .Distinct()
        .Where(word => vowels.Contains(Char.ToLower(word[0])))
        .ToList();

char[] vowels = { 'a', 'e', 'i', 'o', 'u' };

IEnumerable<string> vowelStartWords = strings
    .SelectMany(sentence => sentence.Split(' '))
    .Where(word => Array.IndexOf(vowels, char.ToLower(word[0])) != -1)
;

Console.WriteLine(
    string.Join(
        "\n",
        strings.SelectMany(sentence => sentence.Split(' '))
            .Where(word => Array.IndexOf(vowels, char.ToLower(word[0])) != -1)
            .Select(vowelWord => $"\"{vowelWord}\" starts with a vowel")))
;

public static class EnumerableExtensions
{
    public static void ForEach<T>(this IEnumerable<T> source, Action<T> action)
    {
        if (source == null) throw new ArgumentNullException(nameof(source));
        if (action == null) throw new ArgumentNullException(nameof(action));
        
        foreach (T item in source)
        {
            action(item);
        }
    }
}

strings.SelectMany(sentence => sentence.Split(' '))
    .Where(word => Array.IndexOf(vowels, char.ToLower(word[0])) != -1)
    .Select(vowelWord => $"\"{vowelWord}\" starts with a vowel")
    .ForEach(Console.WriteLine)
;

.Select(vowelWord => Console.WriteLine($"\"{vowelWord}\" starts with a vowel"))

Quote:

The agency has received 31 reports of people hospitalized due to the heart problems, including 10 deaths over the last 39 years.

Mike Hankey wrote:

collateral damage

Daniel Pfeffer wrote:

Have you heard what comes out of their mouths?