The correct answer is A. MessageBox.Show.
MessageBox.Show is a method in the System.Windows.Forms namespace that displays a message box. It takes three parameters: the text of the message, the type of message box, and the buttons that should be displayed.
The type of message box can be one of the following values:
- MessageBoxButtons.OK: A single OK button is displayed.
- MessageBoxButtons.OKCancel: Two buttons, OK and Cancel, are displayed.
- MessageBoxButtons.YesNo: Two buttons, Yes and No, are displayed.
- MessageBoxButtons.YesNoCancel: Three buttons, Yes, No, and Cancel, are displayed.
The buttons that are displayed can be customized by using the MessageBoxButtons enumeration.
The following code shows how to use the MessageBox.Show method to display a message box with the text “Hello, world!” and the OK button:
MessageBox.Show("Hello, world!", "Message Box", MessageBoxButtons.OK);
The following code shows how to use the MessageBox.Show method to display a message box with the text “Do you want to save your changes?” and the Yes, No, and Cancel buttons:
MessageBox.Show("Do you want to save your changes?", "Message Box", MessageBoxButtons.YesNoCancel);