Program.cs

using System;

namespace FourthTask
{
    class Program
    {
        private static string[] _subjects;
        private static string[] _predicates;
        private static string[] _objects;

        static void Main()
        {
            FillArrays();
            StartSentenceGeneration();
        }

        private static void FillArrays()
        {
            _subjects = new[] {"Mom", "Dad", "Grandma", "Grandpa", "Sister", "Brother", "Aunt", "Uncle", "Adam", "Eve"};
            _predicates = new[]
                {
                    "cleans", "prepares", "washes", "serves", "does", "helps", "waters", "paints", "calculates", "searches"
                };
            _objects = new[]
                {
                    "windows", "food", "dishes", "lunch", "a homework", "mom", "the flowerpot", "a wall", "a formula",
                    "a lost item"
                };
        }

        private static void StartSentenceGeneration()
        {
            char key;
            var random = new Random();

            do
            {
                Console.WriteLine("{0} {1} {2}.", _subjects[random.Next(0, _subjects.Length)],
                                  _predicates[random.Next(0, _predicates.Length)],
                                  _objects[random.Next(0, _objects.Length)]);

                key = Console.ReadKey().KeyChar;

                Console.Clear();
            } while (char.ToLower(key) != 'q');
        }
    }
}