Mr Carter says we can't tell people about the steps in the sand. He says they're very important.

----------------------------
Does #1 as in the passage above mean #2, #3, or #4??

1. We can't tell people about the steps.
2. We are not able to tell people about the steps.
3. We mayn't tell people about the steps.
4. We must not tell people about the steps.

1 and 3 and 4 have the same meaning in this context.