Punctuation

I believe that each of the six sentences below is punctuated correctly. Do you agree?

1. The questions 'What was his reason?', 'What did he have to gain?' and 'Why did he do it?' will remain forever unanswered.

2. The questions 'Who?', 'What?', 'When?', 'Where?', 'How?' and 'Why?' need to be answered before you proceed with your investigation.

3. Your last question, 'How can we improve communications between departments?', can best be answered by you.

4. An exciting article -- 'Can Cancer Now Be Cured?' -- appears in the magazine I'm enclosing.

5. An exciting article, 'Can Cancer Now Be Cured?', appears in the magazine I'm enclosing.

Thank you.

6. The weekly book, "Who's Afraid of Virginia Woolf?", is now on sale.

Thanks.