I said, “Lord, how could that be?”: For addressing an angel as Lord, see the comments on 2 Esd 2.44. How could that be? is a rhetorical question, which Good News Bible renders as a strong statement. Good News Bible may be used as a model for this verse. Another possible one is:

• “No, Lord,” I answered. “That would make no sense [or, That would be a stupid thing to do].”

Quoted with permission from Bullard, Roger A. and Hatton, Howard A. A Handbook on 1-2 Esdras. (UBS Helps for Translators). Miami: UBS, 2019. For this and other handbooks for translators see here.