以下程序的运行结果是 。 Dim x As Integer, y As Integer, z As Integer Sub s1(a As Integer, b As Integer) Dim c As Integer a = 2 * a b = b + 2 c = a + b End Sub Sub s2(a As Integer, ByVal b As Integer) Dim c As Integer a = 2 * a b = b + 2 c = a + b End Sub Private Sub Command1_Click() x = 4 y = 4 z = 6 Call s1(x, y) Print x + y + z; Call s2(x, y) Print x + y + z End Sub A. 24 28 B. 20 28 C. 20 18 D. 20 20