private void GameScreen_KeyDown(object sender, KeyEventArgs e)
        {
            bool?  correct = null; // (datatype)? specifies a version of that datatype that can have the value null
            string key     = e.KeyData.ToString();

            if (key == "Escape")
            {
                this.Close();
            }
            if (!CoverLabel1.Visible)
            {
                switch (key)
                {
                case "A": correct = Q1.CheckAnswer(LeftAnswer1.Text); break;

                case "D": correct = Q1.CheckAnswer(RightAnswer1.Text); break;

                case "W": correct = Q1.CheckAnswer(UpAnswer1.Text); break;

                case "S": correct = Q1.CheckAnswer(DownAnswer1.Text); break;
                }
                if (correct != null)
                {
                    if (correct == true)
                    {
                        CoverLabel1.Text      = GoodText[r.Next(0, 6)];
                        CoverLabel1.ForeColor = Color.Green;
                        car1.X    += 2;
                        car1.Speed = 4;
                    }
                    else
                    {
                        CoverLabel1.Text      = BadText[r.Next(0, 6)];
                        CoverLabel1.ForeColor = Color.Red;
                        car1.X    += 1;
                        car1.Speed = 1;
                        if (_sfx)
                        {
                            SystemSounds.Hand.Play();
                        }
                    }
                    CoverLabel1.Show();
                    questionTimer1.Stop();
                    TPQList1.Add(questionTimer1.Elapsed.TotalSeconds);
                    return;
                }
            }
            if (!CoverLabel2.Visible)
            {
                switch (key)
                {
                case "Left": correct = Q2.CheckAnswer(LeftAnswer2.Text); break;

                case "Right": correct = Q2.CheckAnswer(RightAnswer2.Text); break;

                case "Up": correct = Q2.CheckAnswer(UpAnswer2.Text); break;

                case "Down": correct = Q2.CheckAnswer(DownAnswer2.Text); break;
                }
                if (correct != null)
                {
                    if (correct == true)
                    {
                        CoverLabel2.Text      = GoodText[r.Next(0, 6)];
                        CoverLabel2.ForeColor = Color.Green;
                        car2.X    += 2;
                        car2.Speed = 4;
                    }
                    else
                    {
                        CoverLabel2.Text      = BadText[r.Next(0, 6)];
                        CoverLabel2.ForeColor = Color.Red;
                        car2.X    += 1;
                        car2.Speed = 1;
                        if (_sfx)
                        {
                            SystemSounds.Hand.Play();
                        }
                    }
                    CoverLabel2.Show();
                    questionTimer2.Stop();
                    TPQList2.Add(questionTimer2.Elapsed.TotalSeconds);
                    return;
                }
            }
        }