punctuation - Is a question mark needed at the end of a question if the sentence ends with a period or an exclamation mark?

For example, in the two sentences below, are you supposed to end with a question mark?

Which of Shaw's plays has the line "If only parents would realize how they bore their children!"

And

Is the next board-meeting going to be held in Washington, D.C.

Edit: Why do I ask? Because the Webster's New World College Dictionary (3rd edition) that I have at home says if two marks of punctuation are needed at the same place within a sentence, 'only the stronger is usually retained'. And they give the first sentence as an example, omitting the question mark. I made up the second example. There's nothing said about how to decide which is stronger.