| Aren't you forgetting about X? |
| Be that as it may, what about X? |
| Do you happen to know about X? |
| Do you seriously believe X? |
| Do you seriously believe that X? |
| I have a question about X. |
| I'm not sure I understand. |
| Tell me more about X? |
| The question still remains as to X. |
| What about X? |
| What's up? |
| Wouldn't that be related to X? |