Hey there! I'm happy to help!
When Moses wanted to escape Egypt with his people God said he would bring a curse among all of the firstborn sons, killing them. However, God promised the Jewish people that if they put lambs blood on their door he would spare those firstborns sons and the angel of death would pass over those homes.
This looks like it could be both A and D, but a covenant and promise isn't an event. So, the answer is A. The final plague in Egypt during the Exodus,
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