Fill in the blanks with appropriate modals:

We…………………. obey our elders

must

The correct answer is OPTION 2 -  must

In the sentence, "We must obey our elders," the modal "must" expresses a strong obligation or necessity to obey. While "have to" could also fit, it is generally less strong than "must." The other options (might and has to) are not suitable in this context.